AQL Syntax

Query types

An AQL query must either return a result (indicated by usage of the RETURN keyword) or execute a data-modification operation (indicated by usage of one of the keywords INSERT, UPDATE, REPLACE, REMOVE or UPSERT). The AQL parser will return an error if it detects more than one data-modification operation in the same query or if it cannot figure out if the query is meant to be a data retrieval or a modification operation.

AQL only allows one query in a single query string; thus semicolons to indicate the end of one query and separate multiple queries (as seen in SQL) are not allowed.

Whitespace

Whitespace (blanks, carriage returns, line feeds, and tab stops) can be used in the query text to increase its readability. Tokens have to be separated by any number of whitespace. Whitespace within strings or names must be enclosed in quotes in order to be preserved.

Comments

Comments can be embedded at any position in a query. The text contained in the comment is ignored by the AQL parser.

Multi-line comments cannot be nested, which means subsequent comment starts within comments are ignored, comment ends will end the comment.

AQL supports two types of comments:

• Single line comments: These start with a double forward slash and end at the end of the line, or the end of the query string (whichever is first).
• Multi line comments: These start with a forward slash and asterisk, and end with an asterisk and a following forward slash. They can span as many lines as necessary.

/* this is a comment */ RETURN 1
/* these */ RETURN /* are */ 1 /* multiple */ + /* comments */ 1
/* this is
   a multi line
   comment */
// a single line comment

Keywords

On the top level, AQL offers the following high-level operations:

Each of the above operations can be initiated in a query by using a keyword of the same name. An AQL query can (and typically does) consist of multiple of the above operations.

An example AQL query may look like this:

FOR u IN users
  FILTER u.type == "newbie" && u.active == true
  RETURN u.name

In this example query, the terms FOR, FILTER, and RETURN initiate the higher-level operation according to their name. These terms are also keywords, meaning that they have a special meaning in the language.

For example, the query parser will use the keywords to find out which high-level operations to execute. That also means keywords can only be used at certain locations in a query. This also makes all keywords reserved words that must not be used for other purposes than they are intended for.

For example, it is not possible to use a keyword as literal unquoted string (identifier) for a collection or attribute name. If a collection or attribute needs to have the same name as a keyword, then the collection or attribute name needs to be quoted / escaped in the query (also see Names).

Keywords are case-insensitive, meaning they can be specified in lower, upper, or mixed case in queries. In this documentation, all keywords are written in upper case to make them distinguishable from other query parts.

There are a few more keywords in addition to the higher-level operation keywords. Additional keywords may be added in future versions of ArangoDB. The complete list of keywords is currently:

• AGGREGATE
• ALL
• AND
• ANY
• ASC
• COLLECT
• DESC
• DISTINCT
• FALSE
• FILTER
• FOR
• GRAPH
• IN
• INBOUND
• INSERT
• INTO
• K_PATHS
• K_SHORTEST_PATHS
• LET
• LIKE
• LIMIT
• NONE
• NOT
• NULL
• OR
• OUTBOUND
• REMOVE
• REPLACE
• RETURN
• SHORTEST_PATH
• SORT
• TRUE
• UPDATE
• UPSERT
• WITH
• WINDOW

On top of that, there are a few words used in language constructs which are not reserved keywords. They may thus be used as collection or attribute names without quoting or escaping. The query parser can identify them as keyword-like based on the context:

• KEEP – COLLECT operation variant
• COUNT (WITH COUNT INTO) – COLLECT operation variant
• OPTIONS – FOR / Graph Traversal / SEARCH / COLLECT / INSERT / UPDATE / REPLACE / UPSERT / REMOVE operation
• PRUNE – Graph Traversal, FOR operation variant
• SEARCH – SEARCH operation
• TO – Shortest Path / All Shortest Paths / k Shortest Paths / k Paths graph traversal

Last but not least, there are special variables which are available in certain contexts. Unlike keywords, they are case-sensitive:

• CURRENT – available in array inline expressions
• NEW – available after INSERT / UPDATE / REPLACE / UPSERT operation
• OLD – available after UPDATE / REPLACE / UPSERT / REMOVE operation

If you define a variable with the same name in the same scope, then its value will be and remain at what you set it to. Hence you need to avoid these names for your own variables if you want to access the special variable values.

Names

In general, names are used to identify the following things in AQL queries:

• collections
• attributes
• variables
• functions

Names in AQL are always case-sensitive. The maximum supported length for collection/View names is 256 bytes. Variable names can be longer, but are discouraged.

Keywords must not be used as names. If a reserved keyword should be used as a name, the name must be enclosed in backticks or forward ticks.

FOR doc IN `filter`
  RETURN doc.`sort`

Due to the backticks, filter and sort are interpreted as names and not as keywords here.

You can also use forward ticks:

FOR f IN ´filter´
  RETURN f.´sort´

Instead of ticks, you may use the bracket notation for the attribute access:

FOR f IN `filter`
  RETURN f["sort"]

sort is a quoted string literal in this alternative and does thus not conflict with the reserved word.

Escaping is also required if special characters such as hyphen minus (-) are contained in a name:

FOR doc IN `my-coll`
  RETURN doc

The collection my-coll has a dash in its name, but - is an arithmetic operator for subtraction in AQL. The backticks escape the collection name to refer to the collection correctly. Note that quoting the name with " or ' is not possible for collections.

Collection names

Collection names can be used in queries as they are. If a collection happens to have the same name as a keyword, the name must be enclosed in backticks or forward ticks.

For information about the naming constraints for collections, see Collection names.

AQL currently has a limit of up to 256 collections used in one AQL query. This limit applies to the sum of all involved document and edge collections.

Attribute names

When referring to attributes of documents from a collection, the fully qualified attribute name must be used. This is because multiple collections with ambiguous attribute names may be used in a query. To avoid any ambiguity, it is not allowed to refer to an unqualified attribute name.

Also see the naming restrictions for Attribute names.

FOR u IN users
  FOR f IN friends
    FILTER u.active == true && f.active == true && u.id == f.userId
    RETURN u.name

In the above example, the attribute names active, name, id, and userId are qualified using the collection names they belong to (u and f respectively).

Variable names

AQL allows the user to assign values to additional variables in a query. All variables that are assigned a value must have a name that is unique within the context of the query. Variable names must be different from the names of any collection name used in the same query.

FOR u IN users
  LET friends = u.friends
  RETURN { "name" : u.name, "friends" : friends }

In the above query, users is a collection name, and both u and friends are variable names. This is because the FOR and LET operations need target variables to store their intermediate results.

Allowed characters in variable names are the letters a to z (both in lower and upper case), the numbers 0 to 9, the underscore (_) symbol and the dollar ($) sign. A variable name must not start with a number. If a variable name starts with one or multiple underscore characters, the underscore(s) must be followed by least one letter (a-z or A-Z). The dollar sign can only be used as the very first character in a variable name and must be followed by a letter.