WAIT 和 NOWAIT
MariaDB starting with 10.3.0
从MariaDB 10.3.0开始，引入扩展语法以便下面的语句可以使用innodb_lock_wait_timeout变量和lock_wait_timeout变量设置的锁等待时长：
语法
ALTER TABLE tbl_name [WAIT n|NOWAIT] ... CREATE ... INDEX ON tbl_name (index_col_name, ...) [WAIT n|NOWAIT] ... DROP INDEX ... [WAIT n|NOWAIT] DROP TABLE tbl_name [WAIT n|NOWAIT] ... LOCK TABLE ... [WAIT n|NOWAIT] OPTIMIZE TABLE tbl_name [WAIT n|NOWAIT] RENAME TABLE tbl_name [WAIT n|NOWAIT] ... SELECT ... FOR UPDATE [WAIT n|NOWAIT] SELECT ... LOCK IN SHARE MODE [WAIT n|NOWAIT] TRUNCATE TABLE tbl_name [WAIT n|NOWAIT]
描述
锁等待超时时长可以通过WAIT n(单位为秒)来精确设置，或者设置为NOWAIT，这种情况下，如果无法获取锁会立即返回失败。WAIT 0等价于NOWAIT。
See also
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