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JQPL

· 42 min read
Jack

The Java Persistence Query Language (JPQL) is a platform-independent object-oriented query language defined by JPA. JPQL is similar to SQL, but operates on objects, attributes and relationships instead of tables and columns.

The Java Persistence query language (JPQL) is used to define searches against persistent entities independent of the mechanism used to store those entities. As such, JPQL is "portable", and not constrained to any particular data store (although in some cases it does get constrained). The Java Persistence query language is an extension of the Enterprise JavaBeans query language, EJB QL, adding operations such as bulk deletes and updates, join operations, aggregates, projections, and subqueries. Furthermore, JPQL queries can be declared statically in metadata, or can be dynamically built in code

Caveats​

Avoid GROUPing BY subset of columns from SELECT​

JPQL is not portable when it comes to GROUP BY clause.. Let's say we have query that reads everyone who has lived in Washington. It is common in the U.S., however, that cities share common name. For example, there are more than 80 locations whose names are "Washington". When a person move from Washington, Maine to Washington, Massachusetts, the Address table will have 2 rows with the same combinations of ssn and city columns.

SELECT person
FROM Person person LEFT JOIN Address address ON person.city = address.city
WHERE address.city = "Washington"
GROUP BY person.ssn

This query will work for MySQL but not Oracle, because Oracle requires

JPQL Statement Types​

A JPQL statement may be

  1. a SELECT statement, or
  2. an UPDATE statement,
  3. or a DELETE statement

In BNF syntax, a query language statement is defined as:

QL_statement ::= select_statement | update_statement | delete_statement

JPQL Select Statement​

A select statement is a string which consists of the following clauses:

  • a SELECT clause, which determines the type of the objects or values to be selected;
  • a FROM clause, which provides declarations that designate the domain to which the expressions specified in the other
  • clauses of the query apply;
  • an optional WHERE clause, which may be used to restrict the results that are returned by the query;
  • an optional GROUP BY clause, which allows query results to be aggregated in terms of groups;
  • an optional HAVING clause, which allows filtering over aggregated groups;
  • an optional ORDER BY clause, which may be used to order the results that are returned by the query.

In BNF syntax, a select statement is defined as:

select_statement ::= select_clause from_clause [where_clause] [groupby_clause] [having_clause] [orderby_clause]

JPQL Update and Delete Statements​

Update and delete statements provide bulk operations over sets of entities. In BNF syntax, these operations are defined as:

update_statement ::= update_clause [where_clause]
delete_statement ::= delete_clause [where_clause

JPQL Abstract Schema Types and Query Domains​

The Java Persistence query language is a typed language, and every expression has a type. The type of an expression is derived from the structure of the expression, the abstract schema types of the identification variable declarations, the types to which the persistent fields and relationships evaluate, and the types of literals. The abstract schema type of an entity is derived from the entity class and the metadata information provided by Java language annotations or in the XML descriptor.

Informally, the abstract schema type of an entity can be characterized as follows:

  • For every persistent field or get accessor method (for a persistent property) of the entity class, there is a field ("state-field") whose abstract schema type corresponds to that of the field or the result type of the accessor method.
  • For every persistent relationship field or get accessor method (for a persistent relationship property) of the entity class, there is a field ("association-field") whose type is the abstract schema type of the related entity (or, if the relationship is a one-to-many or many-to-many, a collection of such). Abstract schema types are specific to the query language data model. The persistence provider is not required to implement or otherwise materialize an abstract schema type. The domain of a query consists of the abstract schema types of all entities that are defined in the same persistence unit. The domain of a query may be restricted by the navigability of the relationships of the entity on which it is based. The association-fields of an entity's abstract schema type determine navigability. Using the association-fields and their values, a query can select related entities and use their abstract schema types in the query.

JPQL Entity Naming​

Entities are designated in query strings by their entity names. The entity name is defined by the name element of the Entity annotation (or the entity-name XML descriptor element), and defaults to the unqualified name of the entity class. Entity names are scoped within the persistence unit and must be unique within the persistence unit.

JPQL Schema Example​

This example assumes that the application developer provides several entity classes representing magazines, publishers, authors, and articles. The abstract schema types for these entities are Magazine, Publisher, Author, and Article.

The entity Publisher has a one-to-many relationships with Magazine. There is also a one-to-many relationship between Magazine and Article. The entity Article is related to Author in a one-to-one relationship.

Queries to select magazines can be defined by navigating over the association-fields and state-fields defined by Magazine and Author. A query to find all magazines that have unpublished articles is as follows:

SELECT DISTINCT mag
FROM Magazine AS mag
JOIN mag.articles AS art
WHERE art.published = FALSE

The next query navigates over the association-field authors of the abstract schema type Magazine to find articles, and uses the state-field published of Article to select those magazines that have at least one article that is published. Although predefined reserved identifiers, such as DISTINCT, FROM, AS, JOIN, WHERE, and FALSE, appear in upper case in this example, predefined reserved identifiers are case insensitive. The SELECT clause of this example designates the return type of this query to be of type Magazine. Because the same persistence unit defines the abstract persistence schemas of the related entities, the developer can also specify a query over articles that utilizes the abstract schema type for products, and hence the state-fields and association-fields of both the abstract schema types Magazine and Author. For example, if the abstract schema type Author has a state-field named firstName, a query over articles can be specified using this state-field. Such a query might be to find all magazines that have articles authored by someone with the first name "John".

SELECT DISTINCT mag
FROM Magazine mag
JOIN mag.articles art JOIN art.author auth WHERE auth.firstName = 'John'

Because Magazine is related to Author by means of the relationships between Magazine and Article and between Article and Author, navigation using the association-fields authors and product is used to express the query. This query is specified by using the abstract schema name Magazine, which designates the abstract schema type over which the query ranges. The basis for the navigation is provided by the association-fields authors and product of the abstract schema types Magazine and Article respectively.

JPQL FROM Clause and Navigational Declarations​

The FROM clause of a query defines the domain of the query by declaring identification variables. An identification variable is an identifier declared in the FROM clause of a query. The domain of the query may be constrained by path expressions. Identification variables designate instances of a particular entity abstract schema type. The FROM clause can contain multiple identification variable declarations separated by a comma (,):

  • from_clause ::= FROM identification_variable_declaration {, {identification_variable_declaration | collection_member_declaration}}*
  • identification_variable_declaration ::= range_variable_declaration { join | fetch_join }*
  • range_variable_declaration ::= abstract_schema_name [AS] identification_variable
  • join ::= join_spec join_association_path_expression [AS] identification_variable
  • fetch_join ::= join_spec FETCH join_association_path_expression
  • join_association_path_expression ::= join_collection_valued_path_expression | join_single_valued_association_path_expression
  • join_spec ::= [ LEFT [OUTER] | INNER ] JOIN
  • collection_member_declaration ::= IN (collection_valued_path_expression) [AS] identification_variable

JPQL FROM Identifiers​

An identifier is a character sequence of unlimited length. The character sequence must begin with a Java identifier start character, and all other characters must be Java identifier part characters. An identifier start character is any character for which the method Character.isJavaIdentifierStart returns true. This includes the underscore (_) character and the dollar-sign ($) character. An identifier-part character is any character for which the method Character.isJavaIdentifierPart returns true . The question-mark (?) character is reserved for use by the Java Persistence query language. The following are reserved identifiers:

  • SELECT
  • FROM
  • WHERE
  • UPDATE
  • DELETE
  • JOIN
  • OUTER
  • INNER
  • LEFT
  • GROUP
  • BY
  • HAVING
  • FETCH
  • DISTINCT
  • OBJECT
  • NULL
  • TRUE
  • FALSE
  • NOT
  • AND
  • OR
  • BETWEEN
  • LIKE
  • IN
  • AS
  • UNKNOWN
  • EMPTY
  • MEMBER
  • OF
  • IS
  • AVG
  • MAX
  • MIN
  • SUM
  • COUNT
  • ORDER
  • BY
  • ASC
  • DESC
  • MOD
  • UPPER
  • LOWER
  • TRIM
  • POSITION
  • CHARACTER_LENGTH
  • CHAR_LENGTH
  • BIT_LENGTH
  • CURRENT_TIME
  • CURRENT_DATE
  • CURRENT_TIMESTAMP
  • NEW
  • EXISTS
  • ALL
  • ANY
  • SOME

Reserved identifiers are case insensitive. Reserved identifiers must not be used as identification variables. It is recommended that other SQL reserved words not be used as identification variables in queries, as they may be used as reserved identifiers in future releases of the specification.

JPQL Identification Variables​

An identification variable is a valid identifier declared in the FROM clause of a query. All identification variables must be declared in the FROM clause. Identification variables cannot be declared in other clauses. An identification variable must not be a reserved identifier or have the same name as any entity in the same persistence unit: Identification variables are case insensitive. An identification variable evaluates to a value of the type of the expression used in declaring the variable. For example, consider the previous query:

SELECT DISTINCT mag
FROM Magazine mag JOIN mag.articles art JOIN art.author auth
WHERE auth.firstName = 'John'

In the FROM clause declaration mag.articles art, the identification variable art evaluates to any Article value directly reachable from Magazine. The association-field articles is a collection of instances of the abstract schema type Article and the identification variable art refers to an element of this collection. The type of auth is the abstract schema type of Author. An identification variable ranges over the abstract schema type of an entity. An identification variable designates an instance of an entity abstract schema type or an element of a collection of entity abstract schema type instances. Identification variables are existentially quantified in a query. An identification variable always designates a reference to a single value. It is declared in one of three ways:

  1. in a range variable declaration,
  2. in a join clause, or
  3. in a collection member declaration.

The identification variable declarations are evaluated from left to right in the FROM clause, and an identification variable declaration can use the result of a preceding identification variable declaration of the query string.

JPQL Range Declarations​

The syntax for declaring an identification variable as a range variable is similar to that of SQL; optionally, it uses the AS keyword:

range_variable_declaration ::= abstract_schema_name [AS] identification_variable

Range variable declarations allow the developer to designate a "root" for objects which may not be reachable by navigation. In order to select values by comparing more than one instance of an entity abstract schema type, more than one identification variable ranging over the abstract schema type is needed in the FROM clause.

The following query returns magazines whose prices are greater than the price of magazines published by "Adventure" publishers. This example illustrates the use of two different identification variables in the FROM clause, both of the abstract schema type Magazine. The SELECT clause of this query determines that it is the magazines with prices greater than those of "Adventure" publisher's that are returned.

SELECT DISTINCT mag1
FROM Magazine mag1, Magazine mag2
WHERE mag1.price > mag2.price AND mag2.publisher.name = 'Adventure'

JPQL Path Expressions​

An identification variable followed by the navigation operator (.) and a state-field or association-field is a path expression. The type of the path expression is the type computed as the result of navigation; that is, the type of the state-field or association-field to which the expression navigates. Depending on navigability, a path expression that leads to an association-field may be further composed. Path expressions can be composed from other path expressions if the original path expression evaluates to a single-valued type (not a collection) corresponding to an association-field. Path-expression navigability is composed using "inner join" semantics. That is, if the value of a non-terminal association-field in the path expression is null, the path is considered to have no value, and does not participate in the determination of the result. The syntax for single-valued path expressions and collection-valued path expressions is as follows:

  • single_valued_path_expression ::= state_field_path_expression | single_valued_association_path_expression
  • state_field_path_expression ::= {identification_variable | single_valued_association_path_expression}.state_field
  • single_valued_association_path_expression ::= identification_variable.{single_valued_association_field.}*single_valued_association_field
  • collection_valued_path_expression ::= identification_variable.{single_valued_association_field.}*collection_valued_association_field
  • state_field ::= {embedded_class_state_field.}*simple_state_field

A single_valued_association_field is designated by the name of an association-field in a one-to-one or many-to-one relationship. The type of a single_valued_association_field and thus a single_valued_association_path_expression is the abstract schema type of the related entity. A collection_valued_association_field is designated by the name of an association-field in a one-to-many or a many-to-many relationship. The type of a collection_valued_association_field is a collection of values of the abstract schema type of the related entity. An embedded_class_state_field is designated by the name of an entity-state field that corresponds to an embedded class. Navigation to a related entity results in a value of the related entity's abstract schema type.

The evaluation of a path expression terminating in a state-field results in the abstract schema type corresponding to the Java type designated by the state-field. It is syntactically illegal to compose a path expression from a path expression that evaluates to a collection. For example, if mag designates Magazine, the path expression mag.articles.author is illegal since navigation to authors results in a collection. This case should produce an error when the query string is verified. To handle such a navigation, an identification variable must be declared in the FROM clause to range over the elements of the articles collection. Another path expression must be used to navigate over each such element in the WHERE clause of the query, as in the following query, which returns all authors that have any articles in any magazines:

SELECT DISTINCT art.author
FROM Magazine AS mag, IN(mag.articles) art

JPQL Joins​

An inner join may be implicitly specified by the use of a artesian product in the FROM clause and a join condition in the WHERE clause.

The syntax for explicit join operations is as follows:

  • join ::= join_spec join_association_path_expression [AS] identification_variable
  • fetch_join ::= join_spec FETCH join_association_path_expression
  • join_spec ::= [ LEFT [OUTER] | INNER ] JOIN
  • join_association_path_expression ::= join_collection_valued_path_expression | join_single_valued_association_path_expression

The following inner and outer join operation types are supported.

JPQL Inner Joins (Relationship Joins)​

The syntax for the inner join operation is

[ INNER ] JOIN join_association_path_expression [AS] identification_variable

For example, the query below joins over the relationship between publishers and magazines. This type of join typically equates to a join over a foreign key relationship in the database.

SELECT pub
FROM Publisher pub JOIN pub.magazines mag
WHERE pub.revenue > 1000000

The keyword INNER may optionally be used:

SELECT pub
FROM Publisher pub INNER JOIN pub.magazines mag
WHERE pub.revenue > 1000000

This is equivalent to the following query using the earlier IN construct. It selects those publishers with revenue of over 1 million for which at least one magazine exists:

SELECT OBJECT(pub)
FROM Publisher pub, IN(pub.magazines) mag
WHERE pub.revenue > 1000000

JPQL Outer Joins​

LEFT JOIN and LEFT OUTER JOIN are synonymous. They enable the retrieval of a set of entities where matching values in the join condition may be absent. The syntax for a left outer join is

LEFT [OUTER] JOIN join_association_path_expression [AS] identification_variable

For example:

SELECT pub
FROM Publisher pub LEFT JOIN pub.magazines mag
WHERE pub.revenue > 1000000

The keyword OUTER may optionally be used:

SELECT pub
FROM Publisher pub LEFT OUTER JOIN pub.magazines mags
WHERE pub.revenue > 1000000

An important use case for LEFT JOIN is in enabling the prefetching of related data items as a side effect of a query. This is accomplished by specifying the LEFT JOIN as a FETCH JOIN.

JPQL Fetch Joins​

A FETCH JOIN enables the fetching of an association as a side effect of the execution of a query. A FETCH JOIN is specified over an entity and its related entities. The syntax for a fetch join is

fetch_join ::= [ LEFT [OUTER] | INNER ] JOIN FETCH join_association_path_expression

The association referenced by the right side of the FETCH JOIN clause must be an association that belongs to an entity that is returned as a result of the query. It is not permitted to specify an identification variable for the entities referenced by the right side of the FETCH JOIN clause, and hence references to the implicitly fetched entities cannot appear elsewhere in the query. The following query returns a set of magazines. As a side effect, the associated articles for those magazines are also retrieved, even though they are not part of the explicit query result. The persistent fields or properties of the articles that are eagerly fetched are fully initialized. The initialization of the relationship properties of the articles that are retrieved is determined by the metadata for the Article entity class.

SELECT mag
FROM Magazine mag LEFT JOIN FETCH mag.articles
WHERE mag.id = 1

A fetch join has the same join semantics as the corresponding inner or outer join, except that the related objects specified on the right-hand side of the join operation are not returned in the query result or otherwise referenced in the query. Hence, for example, if magazine id 1 has five articles, the above query returns five references to the magazine 1 entity.

JPQL Collection Member Declarations​

An identification variable declared by a collection_member_declaration ranges over values of a collection obtained by navigation using a path expression. Such a path expression represents a navigation involving the association-fields of an entity abstract schema type. Because a path expression can be based on another path expression, the navigation can use the association-fields of related entities. An identification variable of a collection member declaration is declared using a special operator, the reserved identifier IN. The argument to the IN operator is a collection-valued path expression. The path expression evaluates to a collection type specified as a result of navigation to a collection-valued association-field of an entity abstract schema type. The syntax for declaring a collection member identification variable is as follows:

collection_member_declaration ::= IN (collection_valued_path_expression) [AS] identification_variable

For example, the query

SELECT DISTINCT mag
FROM Magazine mag
    JOIN mag.articles art
    JOIN art.author auth
WHERE auth.lastName = 'Grisham'

may equivalently be expressed as follows, using the IN operator:

SELECT DISTINCT mag
FROM Magazine mag, IN(mag.articles) art
WHERE art.author.lastName = 'Grisham'

In this example, articles is the name of an association-field whose value is a collection of instances of the abstract schema type Article. The identification variable art designates a member of this collection, a single Article abstract schema type instance. In this example, mag is an identification variable of the abstract schema type Magazine.

JPQL Polymorphism​

Java Persistence queries are automatically polymorphic. The FROM clause of a query designates not only instances of the specific entity classes to which the query explicitly refers but of subclasses as well. The instances returned by a query include instances of the subclasses that satisfy the query criteria.

JPQL WHERE Clause​

The WHERE clause of a query consists of a conditional expression used to select objects or values that satisfy the expression. The WHERE clause restricts the result of a select statement or the scope of an update or delete operation. A WHERE clause is defined as follows:

where_clause ::= WHERE conditional_expression

The GROUP BY construct enables the aggregation of values according to the properties of an entity class. The HAVING construct enables conditions to be specified that further restrict the query result as restrictions upon the groups. The syntax of the HAVING clause is as follows:

having_clause ::= HAVING conditional_expression

JPQL Conditional Expressions​

The following sections describe the language constructs that can be used in a conditional expression of the WHERE clause or HAVING clause. State-fields that are mapped in serialized form or as lobs may not be portably used in conditional expressions

note

The implementation is not expected to perform such query operations involving such fields in memory rather than in the database.

JPQL Literals​

A string literal is enclosed in single quotes -- for example: 'literal'. A string literal that includes a single quote is represented by two single quotes -- for example: 'literal''s'. String literals in queries, like Java String literals, use unicode character encoding. The use of Java escape notation is not supported in query string literals. Exact numeric literals support the use of Java integer literal syntax as well as SQL exact numeric literal syntax. Approximate literals support the use Java floating point literal syntax as well as SQL approximate numeric literal syntax. Enum literals support the use of Java enum literal syntax. The enum class name must be specified. Appropriate suffixes may be used to indicate the specific type of a numeric literal in accordance with the Java Language Specification. The boolean literals are TRUE and FALSE. Although predefined reserved literals appear in upper case, they are case insensitive.

JPQL Identification Variables (WHERE/HAVING)​

All identification variables used in the WHERE or HAVING clause of a SELECT or DELETE statement must be declared in the FROM clause, as described in JPQL Identification Variables. The identification variables used in the WHERE clause of an UPDATE statement must be declared in the UPDATE clause. Identification variables are existentially quantified in the WHERE and HAVING clause. This means that an identification variable represents a member of a collection or an instance of an entity's abstract schema type. An identification variable never designates a collection in its entirety.

JPQL Path Expressions (WHERE/HAVING)​

It is illegal to use a collection_valued_path_expression within a WHERE or HAVING clause as part of a conditional expression except in an empty_collection_comparison_expression, in a collection_member_expression, or as an argument to the SIZE operator.

JPQL Input Parameters​

Either positional or named parameters may be used. Positional and named parameters may not be mixed in a single query. Input parameters can only be used in the WHERE clause or HAVING clause of a query.

JPQL Positional Parameters​

The following rules apply to positional parameters.

  • Input parameters are designated by the question mark (?) prefix followed by an integer. For example: ?1.
  • Input parameters are numbered starting from 1. Note that the same parameter can be used more than once in the query string and that the ordering of the use of parameters within the query string need not conform to the order of the positional parameters.
JPQL Named Parameters​

A named parameter is an identifier that is prefixed by the ":" symbol. It follows the rules for identifiers defined in JPQL FROM Identifiers. Named parameters are case sensitive.

SELECT pub
FROM Publisher pub
WHERE pub.revenue > :rev

JPQL Conditional Expression Composition​

Conditional expressions are composed of other conditional expressions, comparison operations, logical operations, path expressions that evaluate to boolean values, boolean literals, and boolean input parameters. Arithmetic expressions can be used in comparison expressions. Arithmetic expressions are composed of other arithmetic expressions, arithmetic operations, path expressions that evaluate to numeric values, numeric literals, and numeric input parameters. Arithmetic operations use numeric promotion. Standard bracketing () for ordering expression evaluation is supported. Conditional expressions are defined as follows:

  • conditional_expression ::= conditional_term | conditional_expression OR conditional_term
  • conditional_term ::= conditional_factor | conditional_term AND conditional_factor
  • conditional_factor ::= [ NOT ] conditional_primary
  • conditional_primary ::= simple_cond_expression | (conditional_expression)
  • simple_cond_expression ::= comparison_expression | between_expression | like_expression | in_expression | null_comparison_expression | empty_collection_comparison_expression | collection_member_expression | exists_expression

Aggregate functions can only be used in conditional expressions in a HAVING clause.

JPQL Operators and Operator Precedence​

The operators are listed below in order of decreasing precedence.

  • Navigation operator (.)
  • Arithmetic operators: +, - unary *, / multiplication and division +, - addition and subtraction
  • Comparison operators : =, >, >=, <, <=, <> (not equal), [NOT] BETWEEN, [NOT] LIKE, [NOT] IN, IS [NOT] NULL, IS [NOT] EMPTY, [NOT] MEMBER [OF]
  • Logical operators: NOT AND OR

The following sections describe other operators used in specific expressions.

JPQL Between Expressions​

The syntax for the use of the comparison operator [NOT] BETWEEN in a conditional expression is as follows:

  • arithmetic_expression [NOT] BETWEEN arithmetic_expression AND arithmetic_expression | string_expression [NOT] BETWEEN string_expression AND string_expression | datetime_expression [NOT] BETWEEN datetime_expression AND datetime_expression

The BETWEEN expression x BETWEEN y AND z is semantically equivalent to y <= x AND x <= z,

JPQL In Expressions​

The syntax for the use of the comparison operator [NOT] IN in a conditional expression is as follows:

  • in_expression ::= state_field_path_expression [NOT] IN ( in_item {, in_item}* | subquery)
  • in_item ::= literal | input_parameter

The state_field_path_expression must have a

  • string,
  • numeric, or
  • enum value.

The literal and/or input_parameter values must be like the same abstract schema type of the state_field_path_expression in type. The results of the subquery must be like the same abstract schema type of the state_field_path_expression in type. For example,, o.country IN ('UK', 'US', 'France')

JPQL Like Expressions​

The syntax for the use of the comparison operator [NOT] LIKE in a conditional expression is as follows:

string_expression [NOT] LIKE pattern_value [ESCAPE escape_character]

The string_expression must have a string value. The pattern_value is a string literal or a string-valued input parameter in which an underscore (_) stands for any single character, a percent (%) character stands for any sequence of characters (including the empty sequence), and all other characters stand for themselves. The optional escape_character is a single-character string literal or a character-valued input parameter (i.e., char or Character) and is used to escape the special meaning of the underscore and percent characters in pattern_value. Examples are:

  • asentence.word LIKE 'l_se' - is true for 'lose' and false for 'loose'
  • aword.underscored LIKE '\_%' ESCAPE '\' - is true for '_foo' and false for 'bar'

JPQL Null Comparison Expressions​

The syntax for the use of the comparison operator IS NULL in a conditional expression is as follows:

{single_valued_path_expression | input_parameter } IS [NOT] NULL

A null comparison expression tests whether or not the single-valued path expression or input parameter is a NULL value.

JPQL Empty Collection Comparison Expressions​

The syntax for the use of the comparison operator IS EMPTY in an empty_collection_comparison_expression is as follows:

  • collection_valued_path_expression IS [NOT] EMPTY

This expression tests whether or not the collection designated by the collection-valued path expression is empty (i.e, has no elements).

For example, the following query will return all magazines that don't have any articles at all:

SELECT mag
FROM Magazine mag
WHERE mag.articles IS EMPTY

If the value of the collection-valued path expression in an empty collection comparison expression is unknown, the value of the empty comparison expression is unknown.

JPQL Collection Member Expressions​

The use of the comparison collection_member_expression is as follows: syntax for the operator MEMBER OF in an

  • collection_member_expression ::= entity_expression [NOT] MEMBER [OF] collection_valued_path_expression
  • entity_expression ::= single_valued_association_path_expression | simple_entity_expression
  • simple_entity_expression ::= identification_variable | input_parameter

This expression tests whether the designated value is a member of the collection specified by the collection-valued path expression. If the collection valued path expression designates an empty collection, the value of the MEMBER OF expression is FALSE and the value of the NOT MEMBER OF expression is TRUE. Otherwise, if the value of the collection-valued path expression or single-valued association-field path expression in the collection member expression is NULL or unknown, the value of the collection member expression is unknown.

JPQL Exists Expressions​

An EXISTS expression is a predicate that is true only if the result of the subquery consists of one or more values and that is false otherwise. The syntax of an exists expression is

  • exists_expression ::= [NOT] EXISTS (subquery)

The use of the reserved word OF is optional in this expression.

JPQL All or Any Expressions​

An ALL conditional expression is a predicate that is true if the comparison operation is true for all values in the result of the subquery or the result of the subquery is empty. An ALL conditional expression is false if the result of the comparison is false for at least one row, and is unknown if neither true nor false. An ANY conditional expression is a predicate that is true if the comparison operation is true for some value in the result of the subquery. An ANY conditional expression is false if the result of the subquery is empty or if the comparison operation is false for every value in the result of the subquery, and is unknown if neither true nor false. The keyword SOME is synonymous with ANY. The comparison operators used with ALL or ANY conditional expressions are =, <, <=, >, >=, <>. The result of the subquery must be like that of the other argument to the comparison operator in type.

all_or_any_expression ::= { ALL | ANY | SOME} (subquery)

The following example select the authors who make the highest salary for their magazine:

SELECT auth
FROM Author auth
WHERE auth.salary >= ALL(SELECT a.salary FROM Author a WHERE a.magazine = auth.magazine)

JPQL Subqueries​

Subqueries may be used in the WHERE or HAVING clause. The syntax for subqueries is as follows:

  • subquery ::= simple_select_clause subquery_from_clause [where_clause] [groupby_clause] [having_clause]
  • Subqueries are restricted to the WHERE and HAVING clauses in this release. Support for subqueries in the FROM clause will be considered in a later release of the specification.
  • simple_select_clause ::= SELECT [DISTINCT] simple_select_expression
  • subquery_from_clause ::= FROM subselect_identification_variable_declaration {, subselect_identification_variable_declaration}*
  • subselect_identification_variable_declaration ::= identification_variable_declaration | association_path_expression [AS] identification_variable | collection_member_declaration
  • simple_select_expression ::= single_valued_path_expression | aggregate_expression | identification_variable

Examples:

SELECT DISTINCT auth
FROM Author auth
WHERE EXISTS (
    SELECT spouseAuth
    FROM Author spouseAuth
    WHERE spouseAuth = auth.spouse
)
SELECT mag
FROM Magazine mag
WHERE (SELECT COUNT(art) FROM mag.articles art) > 10

JPQL Functional Expressions​

The JPQL includes the following built-in functions, which may be used in the WHERE or HAVING clause of a query. If the value of any argument to a functional expression is null or unknown, the value of the functional expression is unknown.

JPQL String Functions​
  • functions_returning_strings ::= CONCAT(string_primar y, string_primary) | SUBSTRING(string_primar y, simple_arithmetic_expression, simple_arithmetic_expression) | TRIM([[trim_specification] [trim_character] FROM] string_primary) | LOWER(string_primar y) | UPPER(string_primar y)
  • trim_specification ::= LEADING | TRAILING | BOTH
  • functions_returning_numerics ::= LENGTH(string_primar y) | LOCATE(string_primar y, string_primar y[, simple_arithmetic_expression])

The CONCAT function returns a string that is a concatenation of its arguments. The second and third arguments of the SUBSTRING function denote the starting position and length of the substring to be returned. These arguments are integers. The first position of a string is denoted by 1. The SUBSTRING function returns a string. The TRIM function trims the specified character from a string. If the character to be trimmed is not specified, it is assumed to be space (or blank). The optional trim_character is a single-character string literal or a character-valued input parameter (i.e., char or Character). If a trim specification is not provided, BOTH is assumed. The TRIM function returns the trimmed string. The LOWER and UPPER functions convert a string to lower and upper case, respectively. They return a string. The LOCATE function returns the position of a given string within a string, starting the search at a specified position. It returns the first position at which the string was found as an integer. The first argument is the string to be located; the second argument is the string to be searched; the optional third argument is an integer that represents the string position at which the search is started (by default, the beginning of the string to be searched). The first position in a string is denoted by "1." If the string is not found, 0 is returned. The LENGTH function returns the length of the string in characters "2." as an integer.

JPQL Arithmetic Functions​
functions_returning_numerics ::= ABS(simple_arithmetic_expression) | SQRT(simple_arithmetic_expression) | MOD(simple_arithmetic_expression, simple_arithmetic_expression) | SIZE(collection_valued_path_expression)

The ABS function takes a numeric argument and returns a number (integer, float, or double) of the same type as the argument to the function. The SQRT function takes a numeric argument and returns a double.

The MOD function takes two integer arguments and returns an integer. The SIZE function returns an integer value, the number of elements of the collection. If the collection is empty, the SIZE function evaluates to zero. Numeric arguments to these functions may correspond to the numeric Java object types as well as the primitive numeric types.

JPQL Datetime Functions​
functions_returning_datetime:= CURRENT_DATE | CURRENT_TIME | CURRENT_TIMESTAMP

The datetime functions return the value of current date, time, and timestamp on the database server.

JPQL GROUP BY, HAVING​

The GROUP BY construct enables the aggregation of values according to a set of properties. The HAVING construct enables conditions to be specified that further restrict the query result. Such conditions are restrictions upon the groups. The syntax of the GROUP BY and HAVING clauses is as follows:

  • groupby_clause ::= GROUP BY groupby_item {, groupby_item}*
  • groupby_item ::= single_valued_path_expression | identification_variable
  • having_clause ::= HAVING conditional_expression

If a query contains both a WHERE clause and a GROUP BY clause, the effect is that of first applying the where clause, and then forming the groups and filtering them according to the HAVING clause. The HAVING clause causes those groups to be retained that satisfy the condition of the HAVING clause. The requirements for the SELECT clause when GROUP BY is used follow those of SQL: namely, any item that appears in the SELECT clause (other than as an argument to an aggregate function) must also appear in the GROUP BY clause. In forming the groups, null values are treated as the same for grouping purposes. Grouping by an entity is permitted. In this case, the entity must contain no serialized state fields or lob-valued state fields. The HAVING clause must specify search conditions over the grouping items or aggregate functions that apply to grouping items.

JPQL SELECT Clause​

The SELECT clause denotes the query result. More than one value may be returned from the SELECT clause of a query. The SELECT clause may contain one or more of the following elements:

  • a single range variable or identification variable that ranges over an entity abstract schema type,
  • a single-valued path expression,
  • an aggregate select expression,
  • a constructor expression.

The SELECT clause has the following syntax:

  • select_clause ::= SELECT [DISTINCT] select_expression {, select_expression}*
  • select_expression ::= single_valued_path_expression | aggregate_expression | identification_variable | OBJECT(identification_variable) | constructor_expression
  • constructor_expression ::= NEW constructor_name ( constructor_item {, constructor_item}* )
  • constructor_item ::= single_valued_path_expression | aggregate_expression
  • aggregate_expression ::= { AVG | MAX | MIN | SUM } ([DISTINCT] state_field_path_expression) | COUNT ([DISTINCT] identification_variable | state_field_path_expression | single_valued_association_path_expression)

For example:

SELECT pub.id, pub.revenue
FROM Publisher pub JOIN pub.magazines mag
WHERE mag.price > 5.00
warning

⚠️ Note that the SELECT clause must be specified to return only single-valued expressions. The query below is therefore not valid

SELECT mag.authors
FROM Magazine AS mag

The DISTINCT keyword is used to specify that duplicate values must be eliminated from the query result. If DISTINCT is not specified, duplicate values are not eliminated. Standalone identification variables in the SELECT clause may optionally be qualified by the OBJECT operator. The SELECT clause must not use the OBJECT operator to qualify path expressions.

JPQL Result Type of the SELECT Clause​

The type of the query result specified by the SELECT clause of a query is an entity abstract schema type, a state-field type, the result of an aggregate function, the result of a construction operation, or some sequence of these. The result type of the SELECT clause is defined by the the result types of the select_expressions contained in it. When multiple select_expressions are used in the SELECT clause, the result of the query is of type Object[], and the elements in this result correspond in order to the order of their specification in the SELECT clause and in type to the result types of each of the select_expressions. The type of the result of a select_expression is as follows:

  • A single_valued_path_expression that is a state_field_path_expression results in an object of the same type as the corresponding state field of the entity. If the state field of the entity is a primitive type, the corresponding object type is returned.
  • single_valued_path_expression that is a single_valued_association_path_expression results in an entity object of the type of the relationship field or the subtype of the relationship field of the entity object as determined by the object/relational mapping.
  • The result type of an identification_variable is the type of the entity to which that identification variable corresponds or a subtype as determined by the object/relational mapping.
  • The result type of aggregate_expression is defined in JPQL Aggregate Functions
  • The result type of a constructor_expression is the type of the class for which the constructor is defined. The types of the arguments to the constructor are defined by the above rules.

JPQL Constructor Expressions​

In the SELECT Clause a constructor may be used in the SELECT list to return one or more Java instances. The specified class is not required to be an entity or to be mapped to the database. The constructor name must be fully qualified.

If an entity class name is specified in the SELECT NEW clause, the resulting entity instances are in the new state.

SELECT NEW com.company.PublisherInfo(pub.id, pub.revenue, mag.price)
FROM Publisher pub JOIN pub.magazines mag
WHERE mag.price > 5.00

JPQL Null Values in the Query Result​

If the result of a query corresponds to an association-field or state-field whose value is null, that null value is returned in the result of the query method. The IS NOT NULL construct can be used to eliminate such null values from the result set of the query.

note

State-field types defined in terms of Java numeric primitive types cannot produce NULL values in the query result. A query that returns such a state-field type as a result type must not return a null value.

JPQL Aggregate Functions​

In the SELECT clause the result of a query may be the result of an aggregate function applied to a path expression. The following aggregate functions can be used in the SELECT clause of a query:

  • AVG
  • COUNT
  • MAX
  • MIN
  • SUM

For all aggregate functions except COUNT, the path expression that is the argument to the aggregate function must terminate in a state-field. The path expression argument to COUNT may terminate in either a state-field or an association-field, or the argument to COUNT may be an identification variable. Arguments to the functions SUM and AVG must be numeric. Arguments to the functions MAX and MIN must correspond to orderable state-field types (i.e., numeric types, string types, character types, or date types). The Java type that is contained in the result of a query using an aggregate function is as follows:

  • COUNT returns Long.
  • MAX & MIN return the type of the state-field to which they are applied.
  • AVG returns Double.
  • SUM returns Long when applied to state-fields of integral types (other than BigInteger); Double when applied to state-fields of floating point types; BigInteger when applied to state-fields of type BigInteger; and BigDecimal when applied to state-fields of type BigDecimal.

If SUM, AVG, MAX, or MIN is used, and there are no values to which the aggregate function can be applied, the result of the aggregate function is NULL. If COUNT is used, and there are no values to which COUNT can be applied, the result of the aggregate function is 0.

The argument to an aggregate function may be preceded by the keyword DISTINCT to specify that duplicate values are to be eliminated before the aggregate function is applied. Null values are eliminated before the aggregate function is applied, regardless of whether the keyword DISTINCT is specified.

JPQL ORDER BY Clause​

The ORDER BY clause allows the objects or values that are returned by the query to be ordered. The syntax of the ORDER BY clause is

  • orderby_clause ::= ORDER BY orderby_item {, orderby_item}*
  • orderby_item ::= state_field_path_expression [ASC | DESC]

It is legal to specify DISTINCT with MAX or MIN, but it does not affect the result.

When the ORDER BY clause is used in a query, each element of the SELECT clause of the query must be one of the following:

  • an identification variable x, optionally denoted as OBJECT(x),
  • a single_valued_association_path_expression, or a state_field_path_expression. For example: SELECT pub FROM Publisher pub JOIN pub.magazines mag ORDER BY o.revenue, o.name

If more than one orderby-item is specified, the left-to-right sequence of the orderby-item elements determines the precedence, whereby the leftmost orderby-item has highest precedence. The keyword ASC specifies that ascending ordering be used; the keyword DESC specifies that descending ordering be used. Ascending ordering is the default. SQL rules for the ordering of null values apply: that is, all null values must appear before all non-null values in the ordering or all null values must appear after all non-null values in the ordering, but it is not specified which. The ordering of the query result is preserved in the result of the query method if the ORDER BY clause is used.

JPQL Bulk Update and Delete​

Operations Bulk update and delete operations apply to entities of a single entity class (together with its subclasses, if any). Only one entity abstract schema type may be specified in the FROM or UPDATE clause. The syntax of these operations is as follows:

  • update_statement ::= update_clause [where_clause]
  • update_clause ::= UPDATE abstract_schema_name [[AS] identification_variable] SET update_item {, update_item}*
  • update_item ::= [identification_variable.]{state_field | single_valued_association_field} = new_value
  • new_value ::= simple_arithmetic_expression | string_primary | datetime_primary | boolean_primary | enum_primary simple_entity_expression | NULL
  • delete_statement ::= delete_clause [where_clause]
  • delete_clause ::= DELETE FROM abstract_schema_name [[AS] identification_variable]

The syntax of the WHERE clause is described in JPQL WHERE Clause. A delete operation only applies to entities of the specified class and its subclasses. It does not cascade to related entities. The new_value specified for an update operation must be compatible in type with the state-field to which it is assigned. Bulk update maps directly to a database update operation, bypassing optimistic locking checks. Portable applications must manually update the value of the version column, if desired, and/or manually validate the value of the version column. The persistence context is not synchronized with the result of the bulk update or delete. Caution should be used when executing bulk update or delete operations because they may result in inconsistencies between the database and the entities in the active persistence context. In general, bulk update and delete operations should only be performed within a separate transaction or at the beginning of a transaction (before entities have been accessed whose state might be affected by such operations).

JPQL Null Values​

When the target of a reference does not exist in the database, its value is regarded as NULL. SQL 92 NULL semantics defines the evaluation of conditional expressions containing NULL values. The following is a brief description of these semantics:

  • Comparison or arithmetic operations with a NULL value always yield an unknown value.
  • Two NULL values are not considered to be equal, the comparison yields an unknown value.
  • Comparison or arithmetic operations with an unknown value always yield an unknown value.
  • The IS NULL and IS NOT NULL operators convert a NULL state-field or single-valued association-field value into the respective TRUE or FALSE value.
info

The JPQL defines the empty string, "", as a string with 0 length, which is not equal to a NULL value. However, NULL values and empty strings may not always be distinguished when queries are mapped to some databases. Application developers should therefore not rely on the semantics of query comparisons involving the empty string and NULL value.

JPQL Equality and Comparison Semantics​

Only the values of like types are permitted to be compared. A type is like another type if they correspond to the same Java language type, or if one is a primitive Java language type and the other is the wrappered Java class type equivalent (e.g., int and Integer are like types in this sense). There is one exception to this rule: it is valid to compare numeric values for which the rules of numeric promotion apply. Conditional expressions attempting to compare non-like type values are disallowed except for this numeric case. Note that the arithmetic operators and comparison operators are permitted to be applied to state-fields and input parameters of the wrappered Java class equivalents to the primitive numeric Java types. Two entities of the same abstract schema type are equal if and only if they have the same primary key value. Only equality/inequality comparisons over enums are required to be supported.

The Complete JPQL BNF​

The following is the BNF for the Java Persistence query language, from section 4.14 of the JSR 220 specification.

  • QL_statement ::= select_statement | update_statement | delete_statement
  • select_statement ::= select_clause from_clause [where_clause] [groupby_clause] [having_clause] [orderby_clause]
  • update_statement ::= update_clause [where_clause]
  • delete_statement ::= delete_clause [where_clause]
  • from_clause ::= FROM identification_variable_declaration {, {identification_variable_declaration | collection_member_declaration}}*
  • identification_variable_declaration ::= range_variable_declaration { join | fetch_join }*
  • range_variable_declaration ::= abstract_schema_name [AS] identification_variable
  • join ::= join_spec join_association_path_expression [AS] identification_variable
  • fetch_join ::= join_spec FETCH join_association_path_expression
  • association_path_expression ::= collection_valued_path_expression | single_valued_association_path_expression
  • join_spec ::= [LEFT [OUTER]|INNER] JOIN
  • join_association_path_expression ::= join_collection_valued_path_expression | join_single_valued_association_path_expression
  • join_collection_valued_path_expression ::= identification_variable.collection_valued_association_field
  • join_single_valued_association_path_expression ::= identification_variable.single_valued_association_field
  • collection_member_declaration ::= IN (collection_valued_path_expression) [AS] identification_variable
  • single_valued_path_expression ::= state_field_path_expression | single_valued_association_path_expression
  • state_field_path_expression ::= {identification_variable | single_valued_association_path_expression}.state_field
  • single_valued_association_path_expression ::= identification_variable.{single_valued_association_field.}* single_valued_association_field
  • collection_valued_path_expression ::= identification_variable.{single_valued_association_field.}*collection_valued_association_field
  • state_field ::= {embedded_class_state_field.}*simple_state_field
  • update_clause ::= UPDATE abstract_schema_name [[AS] identification_variable] SET update_item {, update_item}*
  • update_item ::= [identification_variable.]{state_field | single_valued_association_field}= new_value
  • new_value ::= simple_arithmetic_expression | string_primary | datetime_primary | boolean_primary | enum_primary simple_entity_expression | NULL
  • delete_clause ::= DELETE FROM abstract_schema_name [[AS] identification_variable]
  • select_clause ::= SELECT [DISTINCT] select_expression {, select_expression}*
  • select_expression ::= single_valued_path_expression | aggregate_expression | identification_variable | OBJECT(identification_variable)| constructor_expression
  • constructor_expression ::= NEW constructor_name( constructor_item {, constructor_item}*)
  • constructor_item ::= single_valued_path_expression | aggregate_expression
  • aggregate_expression ::= {AVG |MAX |MIN |SUM}([DISTINCT] state_field_path_expression) | COUNT ([DISTINCT] identification_variable | state_field_path_expression | single_valued_association_path_expression)
  • where_clause ::= WHERE conditional_expression
  • groupby_clause ::= GROUP BY groupby_item {, groupby_item}*
  • groupby_item ::= single_valued_path_expression | identification_variable
  • having_clause ::= HAVING conditional_expression
  • orderby_clause ::= ORDER BY orderby_item {, orderby_item}*
  • orderby_item ::= state_field_path_expression [ASC |DESC ]
  • subquery ::= simple_select_clause subquery_from_clause [where_clause] [groupby_clause] [having_clause]
  • subquery_from_clause ::= FROM subselect_identification_variable_declaration {, subselect_identification_variable_declaration}*
  • subselect_identification_variable_declaration ::= identification_variable_declaration | association_path_expression [AS] identification_variable | collection_member_declaration
  • simple_select_clause ::= SELECT [DISTINCT] simple_select_expression
  • simple_select_expression ::= single_valued_path_expression | aggregate_expression | identification_variable
  • conditional_expression ::= conditional_term | conditional_expression OR conditional_term
  • conditional_term ::= conditional_factor | conditional_term AND conditional_factor
  • conditional_factor ::= [NOT ] conditional_primary
  • conditional_primary ::= simple_cond_expression |(conditional_expression)
  • simple_cond_expression ::= comparison_expression | between_expression | like_expression | in_expression | null_comparison_expression | empty_collection_comparison_expression | collection_member_expression | exists_expression
  • between_expression ::= arithmetic_expression [NOT] BETWEEN arithmetic_expression AND arithmetic_expression | string_expression [NOT] BETWEEN string_expression AND string_expression | datetime_expression [NOT] BETWEEN datetime_expression AND datetime_expression
  • in_expression ::= state_field_path_expression [NOT] IN( in_item {, in_item}* | subquery)
  • in_item ::= literal | input_parameter
  • like_expression ::= string_expression [NOT] LIKE pattern_value [ESCAPE escape_character]
  • null_comparison_expression ::= {single_valued_path_expression | input_parameter}IS [NOT] NULL
  • empty_collection_comparison_expression ::= collection_valued_path_expression IS [NOT] EMPTY
  • collection_member_expression ::= entity_expression [NOT] MEMBER [OF] collection_valued_path_expression
  • exists_expression ::= [NOT] EXISTS(subquery)
  • all_or_any_expression ::= {ALL |ANY |SOME}(subquery)
  • comparison_expression ::= string_expressioncomparison_operator{string_expression|all_or_any_expression}| boolean_expression {=|<>} {boolean_expression | all_or_any_expression} | enum_expression {=|<>} {enum_expression | all_or_any_expression} | datetime_expression comparison_operator {datetime_expression | all_or_any_expression} | entity_expression {= |<> } {entity_expression | all_or_any_expression} | arithmetic_expression comparison_operator {arithmetic_expression | all_or_any_expression}
  • comparison_operator ::== |> |>= |< |<= |<>
  • arithmetic_expression ::= simple_arithmetic_expression |(subquery)
  • simple_arithmetic_expression ::= arithmetic_term | simple_arithmetic_expression {+ |- } arithmetic_term
  • arithmetic_term ::= arithmetic_factor | arithmetic_term {* |/ } arithmetic_factor
  • arithmetic_factor ::= [{+ |-}] arithmetic_primary
  • arithmetic_primary ::= state_field_path_expression | numeric_literal | (simple_arithmetic_expression) | input_parameter | functions_returning_numerics | aggregate_expression
  • string_expression ::= string_primary |(subquery)
  • string_primary ::= state_field_path_expression | string_literal | input_parameter | functions_returning_strings | aggregate_expression
  • datetime_expression ::= datetime_primary |(subquery)
  • datetime_primary ::= state_field_path_expression | input_parameter | functions_returning_datetime | aggregate_expression
  • boolean_expression ::= boolean_primary |(subquery)
  • boolean_primary ::= state_field_path_expression | boolean_literal | input_parameter |
  • enum_expression ::= enum_primary |(subquery)
  • enum_primary ::= state_field_path_expression | enum_literal | input_parameter |
  • entity_expression ::= single_valued_association_path_expression | simple_entity_expression
  • simple_entity_expression ::= identification_variable | input_parameter
  • functions_returning_numerics ::= LENGTH(string_primary)| LOCATE(string_primary,string_primary [, simple_arithmetic_expression]) | ABS(simple_arithmetic_expression) | SQRT(simple_arithmetic_expression) | MOD(simple_arithmetic_expression, simple_arithmetic_expression) | SIZE(collection_valued_path_expression)
  • functions_returning_datetime ::= CURRENT_DATE| CURRENT_TIME | CURRENT_TIMESTAMP
  • functions_returning_strings ::= CONCAT(string_primary, string_primary) | SUBSTRING(string_primary, simple_arithmetic_expression,simple_arithmetic_expression)| TRIM([[trim_specification] [trim_character] FROM] string_primary) | LOWER(string_primary) | UPPER(string_primary)
  • trim_specification ::= LEADING | TRAILING | BOTH