Date and time functions

EQL provides functions for working with time, dateTime, and duration data types.

EQL supports normal arithmetic operations between these data types.

All aggregation functions can be applied on these types except for SUM, which cannot be applied to time or dateTime types.

Note: In all cases, the internal representation of dates and times is on an abstract time line with no time zone. On this time line, all days are assumed to have exactly 86400 seconds. The system does not track, nor can it accommodate, leap seconds. This is equivalent to the SQL date, time, and timestamp data types that specify WITHOUT TIMEZONE. ISO 8601 ("Data elements and interchange formats - Information interchange - Representation of dates and times") recommends that, when communicating dates and times without a time zone to other systems, they be represented using Zulu time, which is a synonym for GMT. The Dgraph conforms to this recommendation.

The following table summarizes the supported date and time functions:

Function	Return Data Type	Purpose
`CURRENT_TIMESTAMP` `SYSTIMESTAMP`	`dateTime` `dateTime`	Constants representing the current date and time (at an arbitrary point during query evaluation) in GMT and server time zone, respectively.
`CURRENT_DATE` `SYSDATE`	`dateTime` `dateTime`	Constants representing current date (at an arbitrary point during query evaluation) in GMT and server time zone, respectively.
`TO_TIME` `TO_DATETIME` `TO_DURATION`	`time` `dateTime` `duration`	Constructs a timestamp representing time, date, or duration, using an expression.
`EXTRACT`	`integer`	Extracts a portion of a `dateTime` value, such as the day of the week or month of the year.
`TRUNC`	`dateTime`	Rounds a `dateTime` value down to a coarser granularity.
`TO_TZ` `FROM_TZ`	`dateTime` `dateTime`	Returns the given timestamp in a different time zone.

Note that using CURRENT_DATE, CURRENT_TIMESTAMP, SYSDATE, or SYSTIMESTAMP affects performance because those functions are not cached. The other functions in the table are cached.

The following table summarizes supported operations:

Operation	Return Data Type
`time` (+\|-) `duration`	`time`
`dateTime` (+\|-) `duration`	`dateTime`
`time` - `time`	`duration`
`dateTime` - `dateTime`	`duration`
`duration` (+\|-) `duration`	`duration`
`duration` (*\|/) `double`	`duration`
`duration` /`duration`	`double`