SQL: Implement CURRENT_TIME/CURTIME functions (#40662)

After `TIME` SQL data type is introduced, implement
`CURRENT_TIME/CURTIME` functions similarly to CURRENT_TIMESTAMP
that return the system's current time (only, without the date part).

Closes: #40468
(cherry picked from commit 9feede7)

Author: matriv

docs/reference/sql/appendix/syntax-reserved.asciidoc

@@ -35,6 +35,7 @@ s|SQL-92
 |`CONVERT`                    |reserved      |reserved
 |`CURRENT_DATE`               |reserved      |reserved
 |`CURRENT_TIMESTAMP`          |reserved      |reserved
+|`CURRENT_TIME`               |reserved      |reserved
 |`DAY`                        |reserved      |reserved
 |`DAYS`                       |              |
 |`DESC`                       |reserved      |reserved

docs/reference/sql/functions/date-time.asciidoc

@@ -139,6 +139,63 @@ is used for relative date filtering:
 include-tagged::{sql-specs}/docs/docs.csv-spec[filterToday]
 --------------------------------------------------
 
+[[sql-functions-current-time]]
+==== `CURRENT_TIME/CURTIME`
+
+.Synopsis:
+[source, sql]
+--------------------------------------------------
+CURRENT_TIME
+CURRENT_TIME([precision <1>])
+CURTIME
+--------------------------------------------------
+
+*Input*:
+
+<1> fractional digits; optional
+
+*Output*: time
+
+.Description:
+
+Returns the time when the current query reached the server.
+As a function, `CURRENT_TIME()` accepts _precision_ as an optional
+parameter for rounding the second fractional digits (nanoseconds). The default _precision_ is 3,
+meaning a milliseconds precision current time will be returned.
+
+This method always returns the same value for its every occurrence within the same query.
+
+["source","sql",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{sql-specs}/docs/docs.csv-spec[currentTime]
+--------------------------------------------------
+
+["source","sql",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{sql-specs}/docs/docs.csv-spec[currentTimeFunction]
+--------------------------------------------------
+
+["source","sql",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{sql-specs}/docs/docs.csv-spec[curTimeFunction]
+--------------------------------------------------
+
+["source","sql",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{sql-specs}/docs/docs.csv-spec[currentTimeFunctionPrecision]
+--------------------------------------------------
+
+Typically, this function is used for relative date/time filtering:
+
+["source","sql",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{sql-specs}/docs/docs.csv-spec[filterCurrentTime]
+--------------------------------------------------
+
+[IMPORTANT]
+Currently, using a _precision_ greater than 3 doesn't make any difference to the output of the
+function as the maximum number of second fractional digits returned is 3 (milliseconds).
+
 [[sql-functions-current-timestamp]]
 ==== `CURRENT_TIMESTAMP`
 

docs/reference/sql/functions/index.asciidoc

@@ -49,6 +49,7 @@
 * <<sql-functions-datetime-interval, Date-Time Operators>>
 * <<sql-functions-current-date, Date-Time Functions>>
 ** <<sql-functions-current-date>>
+** <<sql-functions-current-time>>
 ** <<sql-functions-current-timestamp>>
 ** <<sql-functions-datetime-day>>
 ** <<sql-functions-datetime-dow>>

x-pack/plugin/sql/qa/src/main/resources/command.csv-spec

@@ -34,7 +34,9 @@ NULLIF           |CONDITIONAL
 NVL              |CONDITIONAL
 CURDATE          |SCALAR
 CURRENT_DATE     |SCALAR
+CURRENT_TIME     |SCALAR
 CURRENT_TIMESTAMP|SCALAR
+CURTIME          |SCALAR
 DAY              |SCALAR
 DAYNAME          |SCALAR
 DAYOFMONTH       |SCALAR         

x-pack/plugin/sql/qa/src/main/resources/docs/docs.csv-spec

@@ -211,7 +211,9 @@ NULLIF           |CONDITIONAL
 NVL              |CONDITIONAL
 CURDATE          |SCALAR
 CURRENT_DATE     |SCALAR
+CURRENT_TIME     |SCALAR
 CURRENT_TIMESTAMP|SCALAR
+CURTIME          |SCALAR
 DAY              |SCALAR
 DAYNAME          |SCALAR
 DAYOFMONTH       |SCALAR         
@@ -2412,6 +2414,63 @@ Mingsen
 // end::filterToday
 ;
 
+
+currentTime-Ignore
+// tag::currentTime
+SELECT CURRENT_TIME AS result;
+
+         result
+------------------------
+12:31:27.237Z
+// end::currentTime
+;
+
+currentTimeFunction-Ignore
+// tag::currentTimeFunction
+SELECT CURRENT_TIME() AS result;
+
+         result
+------------------------
+12:31:27.237Z
+// end::currentTimeFunction
+;
+
+curTimeFunction-Ignore
+// tag::curTimeFunction
+SELECT CURTIME() AS result;
+
+         result
+------------------------
+12:31:27.237Z
+// end::curTimeFunction
+;
+
+currentTimeFunctionPrecision-Ignore
+// tag::currentTimeFunctionPrecision
+SELECT CURRENT_TIME(1) AS result;
+
+         result
+------------------------
+12:31:27.2Z
+// end::currentTimeFunctionPrecision
+;
+
+
+filterCurrentTime-Ignore
+// tag::filterCurrentTime
+SELECT first_name FROM emp WHERE CAST(hire_date AS TIME) > CURRENT_TIME() - INTERVAL 20 MINUTES ORDER BY first_name ASC LIMIT 5;
+
+  first_name
+---------------
+Alejandro
+Amabile
+Anneke
+Anoosh
+Arumugam
+// end::filterCurrentTime
+;
+
+
 currentTimestamp-Ignore
 // tag::curTs
 SELECT CURRENT_TIMESTAMP AS result;

x-pack/plugin/sql/qa/src/main/resources/time.csv-spec

@@ -81,3 +81,24 @@ SELECT HOUR(CAST('10:11:12.345' AS TIME) + INTERVAL '20' HOURS) AS h, SECOND(INT
 h:i       | m:i
 6         | 52
 ;
+
+orderByCurrentTime
+SELECT first_name FROM test_emp ORDER BY CURRENT_TIME(), first_name LIMIT 5;
+
+  first_name
+---------------
+Alejandro
+Amabile
+Anneke
+Anoosh
+Arumugam
+;
+
+// Awaits Fix https://github.com/elastic/elasticsearch/issues/40639
+groupByCurrentTime-Ignore
+SELECT MAX(salary) FROM test_emp GROUP BY CURRENT_TIME;
+
+  MAX(salary)
+---------------
+74999
+;

x-pack/plugin/sql/src/main/antlr/SqlBase.g4

@@ -226,8 +226,9 @@ primaryExpression
     ;
 
 builtinDateTimeFunction
-    : name=CURRENT_DATE ('(' ')')?
-    | name=CURRENT_TIMESTAMP ('(' precision=INTEGER_VALUE? ')')?
+    : name=CURRENT_TIMESTAMP ('(' precision=INTEGER_VALUE? ')')?
+    | name=CURRENT_DATE ('(' ')')?
+    | name=CURRENT_TIME ('(' precision=INTEGER_VALUE? ')')?
     ;
 
 castExpression
@@ -373,6 +374,7 @@ CATALOGS: 'CATALOGS';
 COLUMNS: 'COLUMNS';
 CONVERT: 'CONVERT';
 CURRENT_DATE : 'CURRENT_DATE';
+CURRENT_TIME : 'CURRENT_TIME';
 CURRENT_TIMESTAMP : 'CURRENT_TIMESTAMP';
 DAY: 'DAY';
 DAYS: 'DAYS';