#打開optimizer_trace
SET optimizer_trace="enabled=on";
#輸入SQL語句
SELECT ...;
#查詢optimizer_trace
SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
#關閉optimizer_trace
SET optimizer_trace="enabled=off";
#打開optimizer_trace
SET optimizer_trace="enabled=on";
#輸入SQL語句
SELECT ...;
#查詢optimizer_trace
SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
#關閉optimizer_trace
SET optimizer_trace="enabled=off";