Other features
The following sections describe some of the other supported features.
String operators
Apart from comparison and concatenation operators Cypher provides special string operators for easier matching of substrings:
| Operator | Description |
|---|---|
a STARTS WITH b | Returns true if the prefix of string a is equal to string b. |
a ENDS WITH b | Returns true if the suffix of string a is equal to string b. |
a CONTAINS b | Returns true if some substring of string a is equal to string b. |
Parameters
When automating the queries for Memgraph, it comes in handy to change only some parts of the query. Usually, these parts are values that are used for filtering results or similar, while the rest of the query remains the same.
Parameters allow reusing the same query but with different parameter values. The
syntax uses the $ symbol to designate a parameter name. We don't allow old
Cypher parameter syntax using curly braces. For example, you can parameterize
filtering a node property:
MATCH (node1 {property: $propertyValue}) RETURN node1;
You can use parameters instead of any literal in the query. Using parameters as
property maps is partially supported in CREATE, but not in MATCH nor MERGE
clause. For example, the following query is illegal:
MATCH (n $propertyMap) RETURN n;
but this is supported:
CREATE (n $propertyMap) RETURN n;
To use parameters with a Python driver use the following syntax:
session.run('CREATE (alice:Person {name: $name, age: $ageValue}',
name='Alice', ageValue=22)).consume()
To use parameters whose names are integers, you will need to wrap parameters in a dictionary and convert them to strings before running a query:
session.run('CREATE (alice:Person {name: $0, age: $1}',
{'0': "Alice", '1': 22})).consume()
To use parameters with some other driver, please consult appropriate documentation.
CASE
Conditional expressions can be expressed in the Cypher language with the CASE
expression. A simple form is used to compare an expression against multiple
predicates. For the first matched predicate result of the expression provided
after the THEN keyword is returned. If no expression is matched value
following ELSE is returned is provided, or null if ELSE is not used:
MATCH (n)
RETURN CASE n.currency WHEN "DOLLAR" THEN "$" WHEN "EURO" THEN "€" ELSE "UNKNOWN" END;
In generic form, you don't need to provide an expression whose value is compared to predicates, but you can list multiple predicates and the first one that evaluates to true is matched:
MATCH (n)
RETURN CASE WHEN n.height < 30 THEN "short" WHEN n.height > 300 THEN "tall" END;
Most expressions that take null as input will produce null. This includes boolean expressions that are used as
predicates. In this case, anything that is not true is interpreted as being false. This also concludes that logically null!=null.
Inspecting and profiling queries
The EXPLAIN and PROFILE clauses can be used to inspect and profile a
particular Cypher query in order to see its internal representation and the way
it behaves during execution:
EXPLAIN MATCH (n) RETURN n;
PROFILE MATCH (n) RETURN n;
For a detailed look at using EXPLAIN and PROFILE, take a look at the guides: