Neo4j - Cypher Manual Study Notes 11

Functions

SHOW FUNCTIONS

Aggregating functions

Function	Signature	Description
avg()	avg(input :: INTEGER | FLOAT | DURATION) :: INTEGER | FLOAT | DURATION	Returns the average of a set of INTEGER, FLOAT, or DURATION values.
collect()	collect(input :: ANY) :: LIST<ANY>	Returns a list containing the values returned by an expression.
count()	count(input :: ANY) :: INTEGER	Returns the number of values or rows.
max()	max(input :: ANY) :: ANY	Returns the maximum value in a set of values.
min()	min(input :: ANY) :: ANY	Returns the minimum value in a set of values.
percentileCont()	percentileCont(input :: FLOAT, percentile :: FLOAT) :: FLOAT	Returns the percentile of a value over a group using linear interpolation.
percentileDisc()	percentileDisc(input :: INTEGER | FLOAT, percentile :: FLOAT) :: FLOAT	Returns the nearest INTEGER or FLOAT value to the given percentile over a group using a rounding method.
stDev()	stDev(input :: FLOAT) :: FLOAT	Returns the standard deviation for the given value over a group for a sample of a population.
stDevP()	stDevP(input :: FLOAT) :: FLOAT	Returns the standard deviation for the given value over a group for an entire population.
sum()	sum(input :: INTEGER | FLOAT | DURATION) :: INTEGER | FLOAT | DURATION	Returns the sum of a set of INTEGER, FLOAT, or DURATION values.

Database functions

Introduced in 5.12

Function	Signature	Description
db.nameFromElementId()	db.nameFromElementId(elementId :: STRING) :: STRING	Resolves the database name from the given element id.

GenAI functions

Introduced in 5.12

Function	Signature	Description
genai.vector.encode()	genai.vector.encode(resource :: STRING, provider :: STRING, configuration :: MAP = {}) :: LIST<FLOAT>	Encode a given resource as a vector using the named provider.

Graph functions

Graph functions provide information about the constituent graphs in composite databases.

Function	Signature	Description
graph.byElementId()	USE graph.byElementId(elementId :: STRING)	Resolves the constituent graph to which a given element id belongs. Introduced in 5.13
graph.byName()	USE graph.byName(name :: STRING)	Resolves a constituent graph by name.
graph.names()	graph.names() :: LIST<STRING>	Returns a list containing the names of all graphs in the current composite database.
graph.propertiesByName()	graph.propertiesByName(name :: STRING) :: MAP	Returns a map containing the properties associated with the given graph.

List functions

Function	Signature	Description
keys()	keys(input :: NODE | RELATIONSHIP | MAP) :: LIST<STRING>	Returns a LIST<STRING> containing the STRING representations for all the property names of a MAP, NODE, or RELATIONSHIP.
labels()	labels(input :: NODE) :: LIST<STRING>	Returns a LIST<STRING> containing the STRING representations for all the labels of a NODE.
nodes()	nodes(input :: PATH) :: LIST<NODE>	Returns a LIST<NODE> containing all the NODE values in a PATH.
range()	range(start :: INTEGER, end :: INTEGER [, step :: INTEGER]) :: LIST<INTEGER>	Returns a LIST<INTEGER> comprising all INTEGER values within a specified range, optionally specifying a step length.
reduce()	reduce(accumulator :: VARIABLE = initial :: ANY, variable :: VARIABLE IN list :: LIST<ANY> expression :: ANY) :: ANY	Runs an expression against individual elements of a LIST<ANY>, storing the result of the expression in an accumulator.
relationships()	relationships(input :: PATH) :: LIST<RELATIONSHIP>	Returns a LIST<RELATIONSHIP> containing all the RELATIONSHIP values in a PATH.
reverse()	reverse(input :: LIST<ANY>) :: LIST<ANY>	Returns a LIST<ANY> in which the order of all elements in the given LIST<ANY> have been reversed.
tail()	tail(input :: LIST<ANY>) :: LIST<ANY>	Returns all but the first element in a LIST<ANY>.
toBooleanList()	toBooleanList(input :: LIST<ANY>) :: LIST<BOOLEAN>	Converts a LIST<ANY> of values to a LIST<BOOLEAN> values. If any values are not convertible to BOOLEAN they will be null in the LIST<BOOLEAN> returned.
toFloatList()	toFloatList(input :: LIST<ANY>) :: LIST<FLOAT>	Converts a LIST<ANY> to a LIST<FLOAT> values. If any values are not convertible to FLOAT they will be null in the LIST<FLOAT> returned.
toIntegerList()	toIntegerList(input :: LIST<ANY>) :: LIST<INTEGER>	Converts a LIST<ANY> to a LIST<INTEGER> values. If any values are not convertible to INTEGER they will be null in the LIST<INTEGER> returned.
toStringList()	toStringList(input :: LIST<ANY>) :: LIST<STRING>	Converts a LIST<ANY> to a LIST<STRING> values. If any values are not convertible to STRING they will be null in the LIST<STRING> returned.

LOAD CSV functions

LOAD CSV functions can be used to get information about the file that is processed by LOAD CSV.

Function	Signature	Description
file()	file() :: STRING	Returns the absolute path of the file that LOAD CSV is using.
linenumber()	linenumber() :: INTEGER	Returns the line number that LOAD CSV is currently using.

Logarithmic functions

These functions all operate on numerical expressions only, and will return an error if used on any other values.

Function	Signature	Description
e()	e() :: FLOAT	Returns the base of the natural logarithm, e.
exp()	exp(input :: FLOAT) :: FLOAT	Returns e^n, where e is the base of the natural logarithm, and n is the value of the argument expression.
log()	log(input :: FLOAT) :: FLOAT	Returns the natural logarithm of a FLOAT.
log10()	log10(input :: FLOAT) :: FLOAT	Returns the common logarithm (base 10) of a FLOAT.
sqrt()	sqrt(input :: FLOAT) :: FLOAT	Returns the square root of a FLOAT.

Numeric functions

These functions all operate on numerical expressions only, and will return an error if used on any other values.

Function	Signature	Description
abs()	abs(input :: INTEGER | FLOAT) :: INTEGER | FLOAT	Returns the absolute value of an INTEGER or FLOAT.
ceil()	ceil(input :: FLOAT) :: FLOAT	Returns the smallest FLOAT that is greater than or equal to a number and equal to an INTEGER.
floor()	floor(input :: FLOAT) :: FLOAT	Returns the largest FLOAT that is less than or equal to a number and equal to an INTEGER.
isNaN()	isNaN(input :: INTEGER | FLOAT) :: BOOLEAN	Returns true if the floating point number is NaN.
rand()	rand() :: FLOAT	Returns a random FLOAT in the range from 0 (inclusive) to 1 (exclusive).
round()	round(input :: FLOAT [, precision :: INTEGER | FLOAT, mode :: STRING]) :: FLOAT	Returns the value of a number rounded to the nearest INTEGER, optionally using a specified precision and rounding mode.
sign()	sign(input :: INTEGER | FLOAT) :: INTEGER	Returns the signum of an INTEGER or FLOAT: 0 if the number is 0, -1 for any negative number, and 1 for any positive number.

Trigonometric functions

These functions all operate on numerical expressions only, and will return an error if used on any other values.

All trigonometric functions operate on radians, unless otherwise specified.

Function	Signature	Description
acos()	acos(input :: FLOAT) :: FLOAT	Returns the arccosine of a FLOAT in radians.
asin()	asin(input :: FLOAT) :: FLOAT	Returns the arcsine of a FLOAT in radians.
atan()	atan(input :: FLOAT) :: FLOAT	Returns the arctangent of a FLOAT in radians.
atan2()	atan2(y :: FLOAT, x :: FLOAT) :: FLOAT	Returns the arctangent2 of a set of coordinates in radians.
cos()	cos(input :: FLOAT) :: FLOAT	Returns the cosine of a FLOAT.
cot()	cot(input :: FLOAT) :: FLOAT	Returns the cotangent of a FLOAT.
degrees()	degrees(input :: FLOAT) :: FLOAT	Converts radians to degrees.
haversin()	haversin(input :: FLOAT) :: FLOAT	Returns half the versine of a number.
pi()	pi() :: FLOAT	Returns the mathematical constant pi.
radians()	radians(input :: FLOAT) :: FLOAT	Converts degrees to radians.
sin()	sin(input :: FLOAT) :: FLOAT	Returns the sine of a FLOAT.
tan()	tan(input :: FLOAT) :: FLOAT	Returns the tangent of a FLOAT.

Predicate functions

These functions return either true or false for the given arguments.

Function	Signature	Description
all()	all(variable :: ANY, list :: LIST<ANY>, predicate :: ANY) :: BOOLEAN	Returns true if the predicate holds for all elements in the given LIST<ANY>.
any()	any(variable :: ANY, list :: LIST<ANY>, predicate :: ANY) :: BOOLEAN	Returns true if the predicate holds for at least one element in the given LIST<ANY>.
exists()	exists(input :: ANY) :: BOOLEAN	Returns true if a match for the pattern exists in the graph.
isEmpty()	isEmpty(input :: LIST<ANY> | MAP | STRING ) :: BOOLEAN	Checks whether the given LIST<ANY>, MAP, or STRING is empty.
none()	none(variable :: ANY, list :: LIST<ANY>, predicate :: ANY) :: BOOLEAN	Returns true if the predicate holds for no element in the given LIST<ANY>.
single()	single(variable :: ANY, list :: LIST<ANY>, predicate :: ANY) :: BOOLEAN	Returns true if the predicate holds for exactly one of the elements in the given LIST<ANY>.

Scalar functions

These functions return a single value.

Function	Signature	Description
char_length()	char_length(input :: STRING) :: INTEGER	Returns the number of Unicode characters in a STRING. Introduced in 5.13
character_length()	character_length(input :: STRING) :: INTEGER	Returns the number of Unicode characters in a STRING. Introduced in 5.13
coalesce()	coalesce(input :: ANY) :: ANY	Returns the first non-null value in a list of expressions.
elementId()	elementId(input :: NODE | RELATIONSHIP) :: STRING	Returns a node or relationship identifier, unique within a specific transaction and DBMS.
endNode()	endNode(input :: RELATIONSHIP) :: NODE	Returns the end NODE of a RELATIONSHIP.
head()	head(list :: LIST<ANY>) :: ANY	Returns the first element in a LIST<ANY>.
id()	id(input :: NODE | RELATIONSHIP) :: INTEGER	Deprecated Returns the id of a NODE or a RELATIONSHIP. Replaced by elementId().
last()	last(list :: LIST<ANY>) :: ANY	Returns the last element in a LIST<ANY>.
length()	length(input :: PATH) :: INTEGER	Returns the length of a PATH.
nullIf()	nullIf(v1 :: ANY, v2 :: ANY) :: ANY	Returns null if the two given parameters are equivalent, otherwise returns the value of the first parameter.
properties()	properties(input :: NODE | RELATIONSHIP | MAP) :: MAP	Returns a MAP containing all the properties of a NODE or RELATIONSHIP.
randomUUID()	randomUUID() :: STRING	Generates a random UUID.
size()	size(input STRING | LIST<ANY>) :: INTEGER	Returns the number of items in a LIST<ANY> or the number of Unicode characters in a STRING.
startNode()	startNode(input :: RELATIONSHIP) :: NODE	Returns the start NODE of a RELATIONSHIP.
toBoolean()	toBoolean(input :: BOOLEAN | STRING | INTEGER) :: BOOLEAN	Converts a BOOLEAN, STRING, or an INTEGER value to a BOOLEAN value.
toBooleanOrNull()	toBooleanOrNull(input :: ANY) :: BOOLEAN	Converts a value to a BOOLEAN value, or null if the value cannot be converted.
toFloat()	toFloat(input :: STRING | INTEGER | FLOAT) :: FLOAT	Converts a STRING or INTEGER value to a FLOAT value.
toFloatOrNull()	toFloatOrNull(input :: ANY) :: FLOAT	Converts a value to a FLOAT value, or null if the value cannot be converted.
toInteger()	toInteger(input :: BOOLEAN | STRING | INTEGER | FLOAT) :: INTEGER	Converts a BOOLEAN, `STRING, or FLOAT value to an INTEGER value.
toIntegerOrNull()	toIntegerOrNull(input :: ANY) :: INTEGER	Converts a value to an INTEGER value, or null if the value cannot be converted.
type()	type(input :: RELATIONSHIP) :: STRING	Returns a STRING representation of the RELATIONSHIP type.
valueType()	valueType(input :: ANY) :: STRING	Returns a STRING representation of the most precise value type that the given expression evaluates to.

String functions

These functions are used to manipulate STRING values or to create a STRING representation of another value.

Function	Signature	Description
btrim()	btrim(original :: STRING [, trimCharacterString :: STRING ]) :: STRING	Returns the given STRING with leading and trailing whitespace removed, optionally specifying a trimCharacterString value to remove. Introduced in 5.20
left()	left(original :: STRING, length :: INTEGER) :: STRING	Returns a STRING containing the specified number (INTEGER) of leftmost characters in the given STRING.
lower()	lower(input :: STRING) :: STRING	Returns the given STRING in lowercase. This function is an alias to the toLower() function, and it was introduced as part of Cypher’s GQL conformance. Introduced in 5.21
ltrim()	ltrim(input :: STRING [, trimCharacterString :: STRING]) :: STRING	Returns the given STRING with leading whitespace removed, optionally specifying a trimCharacterString to remove.
normalize()	normalize(input :: STRING [,normalForm = NFC :: [NFC, NFD, NFKC, NFKD]]) :: STRING	Normalizes a STRING, optionally specifying a normalization form. Introduced in 5.17
replace()	replace(original :: STRING, search :: STRING, replace :: STRING) :: STRING	Returns a STRING in which all occurrences of a specified search STRING in the given STRING have been replaced by another (specified) replacement STRING.
reverse()	reverse(input :: STRING) :: STRING	Returns a STRING in which the order of all characters in the given STRING have been reversed.
right()	right(original :: STRING, length :: INTEGER) :: STRING	Returns a STRING containing the specified number of rightmost characters in the given STRING.
rtrim()	rtrim(input :: STRING [, trimCharacterString :: STRING]) :: STRING	Returns the given STRING with trailing whitespace removed, optionally specifying a trimCharacterString of characters to remove.
split()	split(original :: STRING, splitDelimiters :: LIST<STRING>) :: LIST<STRING>	Returns a LIST<STRING> resulting from the splitting of the given STRING around matches of any of the given delimiters.
substring()	substring(original :: STRING, start :: INTEGER length :: INTEGER) :: STRING	Returns a substring of a given length from the given STRING, beginning with a 0-based index start.
toLower()	toLower(input :: STRING) :: STRING	Returns the given STRING in lowercase.
toString()	toString(input :: ANY) :: STRING	Converts an INTEGER, FLOAT, BOOLEAN, POINT or temporal type (i.e. DATE, ZONED TIME, LOCAL TIME, ZONED DATETIME, LOCAL DATETIME or DURATION) value to a STRING.
toStringOrNull()	toStringOrNull(input :: ANY) :: STRING	Converts an INTEGER, FLOAT, BOOLEAN, POINT or temporal type (i.e. DATE, ZONED TIME, LOCAL TIME, ZONED DATETIME, LOCAL DATETIME or DURATION) value to a STRING, or null if the value cannot be converted.
toUpper()	toUpper(input :: STRING) :: STRING	Returns the given STRING in uppercase.
trim()	trim(trimCharacterString :: STRING, trimSpecification :: STRING, input :: STRING) :: STRING	Returns the given STRING with the leading and/or trailing trimCharacterString character removed.
upper()	upper(input :: STRING) :: STRING	Returns the given STRING in uppercase. This function is an alias to the toUpper() function, and it was introduced as part of Cypher’s GQL conformance. Introduced in 5.21

String normalization is the process of converting text into a standard, consistent format to ensure uniformity and avoid discrepancies caused by different character representations. It is commonly used in text processing, search indexing, and data comparison.

Why Normalize Strings?

1. Unicode Variations: Some characters have multiple valid Unicode representations. For example, é can be:

   • As a single character: U+00E9 (é)
   • As a combination of e and an accent: U+0065 U+0301 (é)

2. Case Sensitivity: Normalizing strings can convert them to a consistent case (e.g., all lowercase or uppercase).

3. Whitespace & Special Characters: Normalization can remove unnecessary spaces, punctuation, or special characters.

Common Forms of Unicode Normalization (NFC, NFD, NFKC, NFKD)

Unicode normalization follows four standard forms:

• NFC (Normalization Form C): Composes characters into their canonical form.
• NFD (Normalization Form D): Decomposes characters into their base form and diacritical marks.
• NFKC (Compatibility Composition): Similar to NFC but also replaces compatibility characters.
• NFKD (Compatibility Decomposition): Similar to NFD but includes compatibility character replacements.

Example in Python

import unicodedata

text = "é"
print(unicodedata.normalize("NFD", text))  # Decomposed form: e + ́
print(unicodedata.normalize("NFC", text))  # Composed form: é

Spatial functions

These functions are used to specify 2D or 3D points in a geographic or cartesian Coordinate Reference System and to calculate the geodesic distance between two points.

Function	Signature	Description
point()	point(input :: MAP) :: POINT	Returns a 2D or 3D point object, given two or respectively three coordinate values in the Cartesian coordinate system or WGS 84 geographic coordinate system.
point.distance()	point.distance(from :: POINT, to :: POINT) :: FLOAT	Returns a FLOAT representing the distance between any two points in the same CRS. If the points are in the WGS 84 CRS, the function returns the geodesic distance (i.e., the shortest path along the curved surface of the Earth). If the points are in a Cartesian CRS, the function returns the Euclidean distance (i.e., the shortest straight-line distance in a flat, planar space).
point.withinBBox()	point.withinBBox(point :: POINT, lowerLeft :: POINT, upperRight :: POINT) :: BOOLEAN	Returns true if the provided point is within the bounding box defined by the two provided points, lowerLeft and upperRight.

Temporal duration functions

DURATION values of the temporal types can be created manipulated using the following functions:

Function	Signature	Description
duration()	duration(input :: ANY) :: DURATION	Constructs a DURATION value.
duration.between()	duration.between(from :: ANY, to :: ANY) :: DURATION	Computes the DURATION between the from instant (inclusive) and the to instant (exclusive) in logical units.
duration.inDays()	duration.inDays(from :: ANY, to :: ANY) :: DURATION	Computes the DURATION between the from instant (inclusive) and the to instant (exclusive) in days.
duration.inMonths()	duration.inMonths(from :: ANY, to :: ANY) :: DURATION	Computes the DURATION between the from instant (inclusive) and the to instant (exclusive) in months.
duration.inSeconds()	duration.inSeconds(from :: ANY, to :: ANY) :: DURATION	Computes the DURATION between the from instant (inclusive) and the to instant (exclusive) in seconds.

 

Temporal instant types functions

Values of the temporal types — DATE, ZONED TIME, LOCAL TIME, ZONED DATETIME, and LOCAL DATETIME — can be created manipulated using the following functions:

Function	Signature	Description
date()	date(input = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: DATE	Creates a DATE instant.
date.realtime()	date.realtime(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: DATE	Returns the current DATE instant using the realtime clock.
date.statement()	date.statement(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: DATE	Returns the current DATE instant using the statement clock.
date.transaction()	date.transaction(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: DATE	Returns the current DATE instant using the transaction clock.
date.truncate()	date.truncate(unit :: STRING, input = DEFAULT_TEMPORAL_ARGUMENT :: ANY, fields = null :: MAP) :: DATE	Truncates the given temporal value to a DATE instant using the specified unit.
datetime()	datetime(input = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: ZONED DATETIME	Creates a ZONED DATETIME instant.
datetime.fromepoch()	datetime.fromepoch(seconds :: INTEGER | FLOAT, nanoseconds :: INTEGER | FLOAT) :: ZONED DATETIME	Creates a ZONED DATETIME given the seconds and nanoseconds since the start of the epoch.
datetime.fromepochmillis()	datetime.fromepochmillis(milliseconds :: INTEGER | FLOAT) :: ZONED DATETIME	Creates a ZONED DATETIME given the milliseconds since the start of the epoch.
datetime.realtime()	datetime.realtime(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: ZONED DATETIME	Returns the current ZONED DATETIME instant using the realtime clock.
datetime.statement()	datetime.statement(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: ZONED DATETIME	Returns the current ZONED DATETIME instant using the statement clock.
datetime.transaction()	datetime.transaction(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: ZONED DATETIME	Returns the current ZONED DATETIME instant using the transaction clock.
datetime.truncate()	datetime.truncate(unit :: STRING, input = DEFAULT_TEMPORAL_ARGUMENT :: ANY, fields = null :: MAP) :: ZONED DATETIME	Truncates the given temporal value to a ZONED DATETIME instant using the specified unit.
localdatetime()	localdatetime(input = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: LOCAL DATETIME	Creates a LOCAL DATETIME instant.
localdatetime.realtime()	localdatetime.realtime(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: LOCAL DATETIME	Returns the current LOCAL DATETIME instant using the realtime clock.
localdatetime.statement()	localdatetime.statement(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: LOCAL DATETIME	Returns the current LOCAL DATETIME instant using the statement clock.
localdatetime.transaction()	localdatetime.transaction(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: LOCAL DATETIME	Returns the current LOCAL DATETIME instant using the transaction clock.
localdatetime.truncate()	localdatetime.truncate(unit :: STRING, input = DEFAULT_TEMPORAL_ARGUMENT :: ANY, fields = null :: MAP) :: LOCAL DATETIME	Truncates the given temporal value to a LOCAL DATETIME instant using the specified unit.
localtime()	localtime(input = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: LOCAL TIME	Creates a LOCAL TIME instant.
localtime.realtime()	localtime.realtime(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: LOCAL TIME	Returns the current LOCAL TIME instant using the realtime clock.
localtime.statement()	localtime.statement(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: LOCAL TIME	Returns the current LOCAL TIME instant using the statement clock.
localtime.transaction()	localtime.transaction(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: LOCAL TIME	Returns the current LOCAL TIME instant using the transaction clock.
localtime.truncate()	localtime.truncate(unit :: STRING, input = DEFAULT_TEMPORAL_ARGUMENT :: ANY, fields = null :: MAP) :: LOCAL TIME	Truncates the given temporal value to a LOCAL TIME instant using the specified unit.
time()	time(input = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: ZONED TIME	Creates a ZONED TIME instant.
time.realtime()	time.realtime(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: ZONED TIME	Returns the current ZONED TIME instant using the realtime clock.
time.statement()	time.statement(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: ZONED TIME	Returns the current ZONED TIME instant using the statement clock.
time.transaction()	time.transaction(timezone = DEFAULT_TEMPORAL_ARGUMENT :: ANY) :: ZONED TIME	Returns the current ZONED TIME instant using the transaction clock.
time.truncate()	time.truncate(unit :: STRING, input = DEFAULT_TEMPORAL_ARGUMENT :: ANY, fields = null :: MAP) :: ZONED TIME	Truncates the given temporal value to a ZONED TIME instant using the specified unit.

 

The realtime, statement, and transaction clocks refer to different ways of tracking time in a database system, particularly in the context of SQL and time-sensitive operations. Here’s what each clock represents:

1. Realtime Clock (date.realtime())

• The realtime clock represents the actual current date and time as observed by the system clock.
• It provides the precise wall-clock time at the moment the function is called.
• This clock is independent of database transactions or queries.

📌 Use Case:

• Logging events based on actual system time.
• Getting the exact current date at the moment of execution.

---

2. Statement Clock (date.statement())

• The statement clock represents the date at the start of the SQL statement execution.
• The value remains constant throughout the execution of the entire SQL statement.
• Even if the statement takes time to execute, the value does not change.

📌 Use Case:

• Ensuring consistency within a single statement.
• Avoiding time inconsistencies in queries that process multiple rows.

---

3. Transaction Clock (date.transaction())

• The transaction clock represents the date at the start of the current transaction.
• It remains constant for the entire transaction duration, even if multiple SQL statements are executed.
• Useful for ensuring all changes within a transaction use the same timestamp.

📌 Use Case:

• Maintaining a consistent timestamp across multiple queries in a transaction.
• Ensuring atomicity in time-sensitive database operations.

---

Comparison Table

Clock Type	Value Changes?	Scope
Realtime (date.realtime())	Yes	Changes every time it's called (real-time system clock).
Statement (date.statement())	No	Constant during the execution of a single SQL statement.
Transaction (date.transaction())	No	Constant throughout the entire transaction.

 

User-defined functions

User-defined functions are written in Java, deployed into the database and are called in the same way as any other Cypher function. There are two main types of functions that can be developed and used:

Type	Description	Usage	Developing
Scalar	For each row the function takes parameters and returns a result.	Using UDF	Extending Neo4j (UDF)
Aggregating	Consumes many rows and produces an aggregated result.	Using aggregating UDF	Extending Neo4j (Aggregating UDF)

Vector functions

Introduced in 5.18

Vector functions allow you to compute the similarity scores of vector pairs.

Function	Signature	Description
vector.similarity.cosine()	vector.similarity.cosine(a :: LIST<INTEGER | FLOAT>, b :: LIST<INTEGER | FLOAT>) :: FLOAT	Returns a FLOAT representing the similarity between the argument vectors based on their cosine.
vector.similarity.euclidean()	vector.similarity.euclidean(a :: LIST<INTEGER | FLOAT>, b :: LIST<INTEGER | FLOAT>) :: FLOAT	Returns a FLOAT representing the similarity between the argument vectors based on their Euclidean distance.