Other Features

The following sections describe some of the other supported features.

UNWIND

The UNWIND clause is used to unwind a list of values as individual rows.

Example. Produce rows out of a single list.

UNWIND [1,2,3] AS listElement RETURN listElement

More examples are here.

Functions

This section contains the list of other supported functions.

Name Description
coalesce Returns the first non null argument.
startNode Returns the starting node of an edge.
endNode Returns the destination node of an edge.
degree Returns the number of edges (both incoming and outgoing) of a node.
head Returns the first element of a list.
last Returns the last element of a list.
properties Returns the properties of a node or an edge.
size Returns the number of elements in a list or a map. When given a string it returns the number of characters. When given a path it returns the number of expansions (edges) in that path.
toBoolean Converts the argument to a boolean.
toFloat Converts the argument to a floating point number.
toInteger Converts the argument to an integer.
type Returns the type of an edge as a character string.
keys Returns a list keys of properties from an edge or a node. Each key is represented as a string of characters.
labels Returns a list of labels from a node. Each label is represented as a character string.
nodes Returns a list of nodes from a path.
relationships Returns a list of relationships (edges) from a path.
range Constructs a list of value in given range.
tail Returns all elements after the first of a given list.
abs Returns the absolute value of a number.
ceil Returns the smallest integer greater than or equal to given number.
floor Returns the largest integer smaller than or equal to given number.
round Returns the number, rounded to the nearest integer. Tie-breaking is done using the commercial rounding, where -1.5 produces -2 and 1.5 produces 2.
exp Calculates e^n where e is the base of the natural logarithm, and n is the given number.
log Calculates the natural logarithm of a given number.
log10 Calculates the logarithm (base 10) of a given number.
sqrt Calculates the square root of a given number.
acos Calculates the arccosine of a given number.
asin Calculates the arcsine of a given number.
atan Calculates the arctangent of a given number.
atan2 Calculates the arctangent2 of a given number.
cos Calculates the cosine of a given number.
sin Calculates the sine of a given number.
tan Calculates the tangent of a given number.
sign Applies the signum function to a given number and returns the result. The signum of positive numbers is 1, of negative -1 and for 0 returns 0.
e Returns the base of the natural logarithm.
pi Returns the constant pi.
rand Returns a random floating point number between 0 (inclusive) and 1 (exclusive).
startsWith Check if the first argument starts with the second.
endsWith Check if the first argument ends with the second.
contains Check if the first argument has an element which is equal to the second argument.
left Returns a string containing the specified number of leftmost characters of the original string.
lTrim Returns the original string with leading whitespace removed.
replace Returns a string in which all occurrences of a specified string in the original string have been replaced by another (specified) string.
reverse Returns a string in which the order of all characters in the original string have been reversed.
right Returns a string containing the specified number of rightmost characters of the original string.
rTrim Returns the original string with trailing whitespace removed.
split Returns a list of strings resulting from the splitting of the original string around matches of the given delimiter.
substring Returns a substring of the original string, beginning with a 0-based index start and length.
toLower Returns the original string in lowercase.
toString Converts an integer, float or boolean value to a string.
toUpper Returns the original string in uppercase.
trim Returns the original string with leading and trailing whitespace removed.
all Check if all elements of a list satisfy a predicate.
The syntax is: all(variable IN list WHERE predicate).
NOTE: Whenever possible, use Memgraph's lambda functions when matching instead.
single Check if only one element of a list satisfies a predicate.
The syntax is: single(variable IN list WHERE predicate).
reduce Accumulate list elements into a single result by applying an expression. The syntax is:
reduce(accumulator = initial_value, variable IN list | expression).
extract A list of values obtained by evaluating an expression for each element in list. The syntax is:
extract(variable IN list | expression).
assert Raises an exception reported to the client if the given argument is not true.
counter Generates integers that are guaranteed to be unique on the database level, for the given counter name.
counterSet Sets the counter with the given name to the given value.
indexInfo Returns a list of all the indexes available in the database. The list includes indexes that are not yet ready for use (they are concurrently being built by another transaction).
timestamp Returns the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.
id Returns identifier for a given node or edge. The identifier is generated during the initialization of node or edge and will be persisted through the durability mechanism.

String Operators

Apart from comparison and concatenation operators openCypher provides special string operators for easier matching of substrings:

Operator Description
a STARTS WITH b Returns true if prefix of string a is equal to string b.
a ENDS WITH b Returns true if 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 which 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, but not instead of property maps even though that is allowed in standard openCypher. Following example is illegal in Memgraph:

MATCH (node1 $propertyValue) RETURN node1

To use parameters with Python driver use following syntax:

session.run('CREATE (alice:Person {name: $name, age: $ageValue}',
            name='Alice', ageValue=22)).consume()

To use parameters which 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 openCypher language by simple and generic form of 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

Have a Question?

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