mysql explain
yaokun123 edited this page Dec 7, 2023
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5 revisions
键 | 值 |
---|---|
id | 选择标识符,id越大最先执行 |
select_type | SIMPLE,PRIMARY, UNION, DEPENDENT UNION,UNION RESULT,SUBQUERY,DEPENDENT SUBQUERY,DERIVED,UNCACHEABLE SUBQUERY |
table | 数据库中表名称 |
type | ALL、index、range、 ref、eq_ref、const、system、NULL(从左到右,性能从差到好) |
possible_keys | 可能用到的索引 |
Key | 实际用到的索引 |
key_len | 索引长度,可以判断复合索引使用情况 |
ref | |
rows | 估算出结果集行数 |
Extra | Using where,Using temporary,Using filesort |
# 1、开启
SET optimizer_trace="enabled=on",end_markers_in_json=on;
# 2、设置记录大小
SET optimizer_trace_max_mem_size=1638400
SELECT create_time FROM person WHERE NAME >'name84059' AND create_time > '2020-05-23 14:39:18';
SELECT * FROM information_schema.OPTIMIZER_TRACE;
# 4、关闭
SET optimizer_trace="enabled=off";