MySQL special statement and optimizer

SQL_NO_CACHE

/*!40001 SQL_NO_CACHE */ means executing SELECT SQL_NO_CACHE * FROM mytable in mysql >= 4.0.1 and not executing the command in earlier versionswith SQL_NO_CACHE.

SELECT /*!40001 SQL_NO_CACHE */ * FROM `test`.`house`;

The query cache was deprecated in MySQL 5.7.20 and removed in MySQL 8.0.

SLEEP

Sleep (pause) duration for the number of seconds given by the parameter, then return 0.Duration may have fractional parts.If the argument is NULL or negative, SLEEP() produces a warning or an error in strict SQL mode.

select *,sleep(n) from table,
If the table record is empty, it will not sleep; if the table record is one, the sleep time is 1n, ifThe table record is x, and the sleep time is: xn.

MAX_EXECUTION_TIME

sql sets the MAX_EXECUTION_TIME parameter to control the execution time of the statement. If the execution is not completed within this time range, the operation will be terminated

show variables like 'max_execution_time'; You can view max_execution_time configuration, MySQL 5.7.8+ version supports this parameter

SELECT /*+ MAX_EXECUTION_TIME(1000) */1 FROM t1 WHERE SLEEP(1000);> ERROR 3024 (HY000): Query execution was interrupted, maximum statement> execution time exceeded

See MySQL Optimizer Hints

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References:

1. SLEEP function
2. Optimizer Hints