LAST_VALUE()
语法
LAST_VALUE(expr,[expr,...])
描述
LAST_VALUE()
对所有表达式求值,并返回最后一个值。
这在结合使用@var:=expr为变量赋值时很有用。例如,当你想要从updated/deleted的行中获取数据时,你无需对表做两次查询。
从MariaDB 10.2.2开始,LAST_FUNCTION可以用作为一个开窗函数window function。
示例
CREATE TABLE t1 (a int, b int); INSERT INTO t1 VALUES(1,10),(2,20); DELETE FROM t1 WHERE a=1 AND last_value(@a:=a,@b:=b,1); SELECT @a,@b; +------+------+ | @a | @b | +------+------+ | 1 | 10 | +------+------+ //译者补充示例 DELETE FROM t1; INSERT INTO t1 VALUES(1,10),(2,20),(1,30); DELETE FROM t1 WHERE a=1 AND last_value(@a:=a,@b:=b,1); SELECT *,@a,@b; +------+------+------+------+ | a | b | @a | @b | +------+------+------+------+ | 2 | 20 | 1 | 30 | +------+------+------+------+
See also
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