Mysql模糊查询优化方法及测试详细讲解

select * from yd_alarminfo_all_20220825 where alarmTitle like "网卡端口%"
--耗时：0.493

-- 创建普通索引
ALTER table yd_alarminfo_all_20220825 add index idx_title(alarmTitle);
-- 查询耗时：0.003

select COUNT(DISTINCT LEFT(alarmTitle,3))/COUNT(*) as sel3,
	COUNT(DISTINCT LEFT(alarmTitle,5))/COUNT(*) as sel5,
	COUNT(DISTINCT LEFT(alarmTitle,7))/COUNT(*) as sel7,
	COUNT(DISTINCT LEFT(alarmTitle,9))/COUNT(*) as sel9,
	COUNT(DISTINCT LEFT(alarmTitle,11))/COUNT(*) as sel11,
	COUNT(DISTINCT LEFT(alarmTitle,13))/COUNT(*) as sel13,
	COUNT(DISTINCT LEFT(alarmTitle,15))/COUNT(*) as sel15,
	COUNT(DISTINCT LEFT(alarmTitle,17))/COUNT(*) as sel17,
	COUNT(DISTINCT LEFT(alarmTitle,19))/COUNT(*) as sel19,
	COUNT(DISTINCT LEFT(alarmTitle,21))/COUNT(*) as sel21
 from yd_alarminfo_all_20220825;

# 删除旧索引
DROP INDEX idx_title ON yd_alarminfo_all_20220825;
# 创建左前缀索引（索引创建语句只比普通索引多了‘(15)'）
ALTER table yd_alarminfo_all_20220825 add index idx_title(alarmTitle(15));
-- 查询耗时：0.01

-- 删除旧索引
DROP INDEX idx_title ON yd_alarminfo_all_20220825;
-- LOCATE
SELECT * FROM yd_alarminfo_all_20220825 WHERE LOCATE('网卡端口', alarmTitle)>0
-- 查询耗时：0.499

SELECT * FROM yd_alarminfo_all_20220825 WHERE POSITION('网卡端口' IN alarmTitle)
--查询耗时：0.544

SELECT * FROM yd_alarminfo_all_20220825 WHERE INSTR(alarmTitle, '网卡端口' )>0
--查询耗时：0.566