谁能帮我解释下这段mysql是做什么的？怎么查询数据库名为[ShFTZNQI]的相关跟踪语句？为什么这段查询会很慢

Question

-- 临时开启慢查询日志
show variables like '%quer%';
set global slow_query_log=1;

-- 临时开启慢查询时间
show variables like 'long_query_time';
set global long_query_time=1;

-- 设置慢查询存储的方式
show variables like 'log_output';
set global log_output = 'FILE';
set global log_output = 'TABLE';

-- 设置查看日志
SELECT * FROM mysql.slow_log;
SELECT * FROM mysql.general_log;

select sleep(30);

explain select ID from new_table;


清空sql日志
SET GLOBAL slow_query_log = 'OFF';
ALTER TABLE mysql.slow_log RENAME mysql.slow_log_drop;
CREATE TABLE mysql.slow_log LIKE mysql.slow_log_drop;
SET GLOBAL slow_query_log = 'ON';
DROP TABLE mysql.slow_log_drop;

SELECT * FROM mysql.slow_log order by start_time desc

Answer 1

慢sql有很多原因,比如没用到索引,数据量太大,语句过于复杂等,建议用explain看一下查询计划