查看优化器状态

show variables like 'optimizer_trace';

会话级别临时开启

 set session optimizer_trace="enabled=on",end_markers_in_json=on;

设置优化器追踪的内存大小

set OPTIMIZER_TRACE_MAX_MEM_SIZE=1000000;

执行自己的SQL

select * from user;

information_schema.optimizer_trace表

SELECT trace FROM information_schema.OPTIMIZER_TRACE;

导入到一个命名为test.trace的文件

 SELECT TRACE INTO DUMPFILE "D:\\test.trace" FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;

不设置优化器最大容量的话，可能会导致优化器返回的结果不全。