Skip to content

Latest commit

 

History

History
519 lines (400 loc) · 11.6 KB

time_functions.md

File metadata and controls

519 lines (400 loc) · 11.6 KB
Raw

Time functions

ZetaSQL supports the following TIME functions.

CURRENT_TIME

CURRENT_TIME([timezone])

Description

Returns the current time as a TIME object. Parentheses are optional when called with no arguments.

This function supports an optional timezone parameter. See Timezone definitions for information on how to specify a time zone.

Return Data Type

TIME

Example

SELECT CURRENT_TIME() as now;

+----------------------------+
| now                        |
+----------------------------+
| 15:31:38.776361            |
+----------------------------+

When a column named current_time is present, the column name and the function call without parentheses are ambiguous. To ensure the function call, add parentheses; to ensure the column name, qualify it with its range variable. For example, the following query will select the function in the now column and the table column in the current_time column.

WITH t AS (SELECT 'column value' AS `current_time`)
SELECT current_time() as now, t.current_time FROM t;

+-----------------+--------------+
| now             | current_time |
+-----------------+--------------+
| 15:31:38.776361 | column value |
+-----------------+--------------+

TIME

1. TIME(hour, minute, second)
2. TIME(timestamp, [timezone])
3. TIME(datetime)

Description

  1. Constructs a TIME object using INT64 values representing the hour, minute, and second.
  2. Constructs a TIME object using a TIMESTAMP object. It supports an optional parameter to specify a timezone. If no timezone is specified, the default timezone, which is implementation defined, is used.
  3. Constructs a TIME object using a DATETIME object.

Return Data Type

TIME

Example

SELECT
  TIME(15, 30, 00) as time_hms,
  TIME(TIMESTAMP "2008-12-25 15:30:00+08", "America/Los_Angeles") as time_tstz;

+----------+-----------+
| time_hms | time_tstz |
+----------+-----------+
| 15:30:00 | 23:30:00  |
+----------+-----------+
SELECT TIME(DATETIME "2008-12-25 15:30:00.000000") AS time_dt;

+----------+
| time_dt  |
+----------+
| 15:30:00 |
+----------+

EXTRACT

EXTRACT(part FROM time_expression)

Description

Returns a value that corresponds to the specified part from a supplied time_expression.

Allowed part values are:

  • NANOSECOND (if the SQL engine supports it)
  • MICROSECOND
  • MILLISECOND
  • SECOND
  • MINUTE
  • HOUR

Returned values truncate lower order time periods. For example, when extracting seconds, EXTRACT truncates the millisecond and microsecond values.

Return Data Type

INT64

Example

In the following example, EXTRACT returns a value corresponding to the HOUR time part.

SELECT EXTRACT(HOUR FROM TIME "15:30:00") as hour;

+------------------+
| hour             |
+------------------+
| 15               |
+------------------+

TIME_ADD

TIME_ADD(time_expression, INTERVAL int64_expression part)

Description

Adds int64_expression units of part to the TIME object.

TIME_ADD supports the following values for part:

  • NANOSECOND (if the SQL engine supports it)
  • MICROSECOND
  • MILLISECOND
  • SECOND
  • MINUTE
  • HOUR

This function automatically adjusts when values fall outside of the 00:00:00 to 24:00:00 boundary. For example, if you add an hour to 23:30:00, the returned value is 00:30:00.

Return Data Types

TIME

Example

SELECT
  TIME "15:30:00" as original_time,
  TIME_ADD(TIME "15:30:00", INTERVAL 10 MINUTE) as later;

+-----------------------------+------------------------+
| original_time               | later                  |
+-----------------------------+------------------------+
| 15:30:00                    | 15:40:00               |
+-----------------------------+------------------------+

TIME_SUB

TIME_SUB(time_expression, INTERVAL int64_expression part)

Description

Subtracts int64_expression units of part from the TIME object.

TIME_SUB supports the following values for part:

  • NANOSECOND (if the SQL engine supports it)
  • MICROSECOND
  • MILLISECOND
  • SECOND
  • MINUTE
  • HOUR

This function automatically adjusts when values fall outside of the 00:00:00 to 24:00:00 boundary. For example, if you subtract an hour from 00:30:00, the returned value is 23:30:00.

Return Data Type

TIME

Example

SELECT
  TIME "15:30:00" as original_date,
  TIME_SUB(TIME "15:30:00", INTERVAL 10 MINUTE) as earlier;

+-----------------------------+------------------------+
| original_date                | earlier                |
+-----------------------------+------------------------+
| 15:30:00                    | 15:20:00               |
+-----------------------------+------------------------+

TIME_DIFF

TIME_DIFF(time_expression_a, time_expression_b, part)

Description

Returns the number of whole specified part intervals between two TIME objects (time_expression_a - time_expression_b). If the first TIME is earlier than the second one, the output is negative. Throws an error if the computation overflows the result type, such as if the difference in nanoseconds between the two TIME objects would overflow an INT64 value.

TIME_DIFF supports the following values for part:

  • NANOSECOND (if the SQL engine supports it)
  • MICROSECOND
  • MILLISECOND
  • SECOND
  • MINUTE
  • HOUR

Return Data Type

INT64

Example

SELECT
  TIME "15:30:00" as first_time,
  TIME "14:35:00" as second_time,
  TIME_DIFF(TIME "15:30:00", TIME "14:35:00", MINUTE) as difference;

+----------------------------+------------------------+------------------------+
| first_time                 | second_time            | difference             |
+----------------------------+------------------------+------------------------+
| 15:30:00                   | 14:35:00               | 55                     |
+----------------------------+------------------------+------------------------+

TIME_TRUNC

TIME_TRUNC(time_expression, part)

Description

Truncates a TIME object to the granularity of part.

TIME_TRUNC supports the following values for part:

  • NANOSECOND (if the SQL engine supports it)
  • MICROSECOND
  • MILLISECOND
  • SECOND
  • MINUTE
  • HOUR

Return Data Type

TIME

Example

SELECT
  TIME "15:30:00" as original,
  TIME_TRUNC(TIME "15:30:00", HOUR) as truncated;

+----------------------------+------------------------+
| original                   | truncated              |
+----------------------------+------------------------+
| 15:30:00                   | 15:00:00               |
+----------------------------+------------------------+

FORMAT_TIME

FORMAT_TIME(format_string, time_object)

Description Formats a TIME object according to the specified format_string. See Supported Format Elements For TIME for a list of format elements that this function supports.

Return Data Type

STRING

Example

SELECT FORMAT_TIME("%R", TIME "15:30:00") as formatted_time;

+----------------+
| formatted_time |
+----------------+
| 15:30          |
+----------------+

PARSE_TIME

PARSE_TIME(format_string, time_string)

Description

Converts a string representation of time to a TIME object.

format_string contains the format elements that define how time_string is formatted. Each element in time_string must have a corresponding element in format_string. The location of each element in format_string must match the location of each element in time_string.

-- This works because elements on both sides match.
SELECT PARSE_TIME("%I:%M:%S", "07:30:00")

-- This doesn't work because the seconds element is in different locations.
SELECT PARSE_TIME("%S:%I:%M", "07:30:00")

-- This doesn't work because one of the seconds elements is missing.
SELECT PARSE_TIME("%I:%M", "07:30:00")

-- This works because %T can find all matching elements in time_string.
SELECT PARSE_TIME("%T", "07:30:00")

The format string fully supports most format elements except for %P.

When using PARSE_TIME, keep the following in mind:

  • Unspecified fields. Any unspecified field is initialized from 00:00:00.0. For instance, if seconds is unspecified then it defaults to 00, and so on.
  • Whitespace. One or more consecutive white spaces in the format string matches zero or more consecutive white spaces in the TIME string. In addition, leading and trailing white spaces in the TIME string are always allowed, even if they are not in the format string.
  • Format precedence. When two (or more) format elements have overlapping information, the last one generally overrides any earlier ones.

Return Data Type

TIME

Example

SELECT PARSE_TIME("%H", "15") as parsed_time;

+-------------+
| parsed_time |
+-------------+
| 15:00:00    |
+-------------+
SELECT PARSE_TIME('%I:%M:%S %p', '2:23:38 PM') AS parsed_time

+-------------+
| parsed_time |
+-------------+
| 14:23:38    |
+-------------+

Supported format elements for TIME

Unless otherwise noted, TIME functions that use format strings support the following elements:

Format element Description Example
%H The hour (24-hour clock) as a decimal number (00-23). 21
%I The hour (12-hour clock) as a decimal number (01-12). 09
%k The hour (24-hour clock) as a decimal number (0-23); single digits are preceded by a space. 21
%l The hour (12-hour clock) as a decimal number (1-12); single digits are preceded by a space. 9
%M The minute as a decimal number (00-59). 47
%n A newline character.
%P Either am or pm. pm
%p Either AM or PM. PM
%R The time in the format %H:%M. 21:47
%r The 12-hour clock time using AM/PM notation. 09:47:00 PM
%S The second as a decimal number (00-60). 00
%T The time in the format %H:%M:%S. 21:47:00
%t A tab character.
%X The time representation in HH:MM:SS format. 21:47:00
%% A single % character. %
%E#S Seconds with # digits of fractional precision. 00.000
%E*S Seconds with full fractional precision (a literal '*'). 00