1.先看一下不加索引的情況
2.然後添加組合索引
ALTER TABLE table_name ADD INDEX index_name (`field_1`,`field_2`);
explain select * from table_name where field_1=1 and field_2=1
看到涉及到的行數變爲了22
3.刪掉組合索引
alter table table_naem drop index enable_xxx
添加兩個單獨索引
ALTER TABLE user_portrait_crm_tag ADD INDEX index_1 (`index_1`);
ALTER TABLE user_portrait_crm_tag ADD INDEX index_2 (`index_2`);
再次執行
explain select * from table_name where field_1=1 and field_2=1
看到rows變爲了29