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FIRST

An aggregate function that returns the first value of a set of input values, defined as the value associated with the minimum time.

Syntax

FIRST (value[, time]);

Arguments

  • value: column value to return
  • time: time expression for comparison. The expression should be one of the following types: DATETIME, DATETIME(6), TIMESTAMP, TIMESTAMP(6). If no time expression is specified, then the SERIES TIMESTAMP is used to defined the time order. Only one SERIES TIMESTAMP can appear in tables used in the query if the time argument is omitted.

Return Type

The first value of a set of input rows, as ordered by the time column.

Remarks

  • If there are multiple instances of the same minimum time expression, then this function returns an arbitrary value from among the values corresponding with that minimum.
  • The function returns an error if there are multiple SERIES TIMESTAMP columns involved, or one is needed due to omission of the time argument but none is present. For example, if more than one table in the FROM clause has a SERIES TIMESTAMP, then it becomes ambiguous which timestamp to use. Hence, the SERIES TIMESTAMP to be used must be specified in the second argument of the FIRST function.

Example

The following examples display the use of FIRST function.

CREATE TABLE table1 (a INT, b DATETIME SERIES TIMESTAMP);
INSERT INTO table1 values (1, "2019-03-14 06:28:00"), (2, "2019-04-14 06:28:00"), (3, "2018-03-14 06:28:00");
SELECT FIRST (a) FROM table1;
+--------------+
| FIRST (a)    |
+--------------+
|            3 |
+--------------+
SELECT FIRST (a, b) FROM table1;
****
+--------------+
| FIRST (a, b) |
+--------------+
|            3 |
+--------------+