查詢重複的字段需要建立索引,多個條件則建立組合索引,各個條件的索引都存在則不必須建立組合索引
有些情況直接使用GROUP BY HAVING則能直接解決;但是有些情況下查詢緩慢,則需要使用下面其他的方法
以下是本人整理出來的查詢重複資料的SQL,适用于千萬級資料量的MYSQL資料庫。
1.适用于整數類型的
SELECT DISTINCT UId FROM vehicle WHERE 1=1 GROUP BY UId HAVING(COUNT(UId))>1;
2.分組排序
SELECT UId FROM
(
SELECT UId,LicenseNo,IF(@grp=a.UId,@rank:[email protected]+1,@rank:=1) rank,@grp:=a.UId FROM
(SELECT UId,LicenseNo FROM vehicle WHERE 1=1 ORDER BY UId) AS a,(SELECT @grp:=0,@rank:=0) AS b
)AS t
WHERE t.rank=2;
3.适用于字元串類型,包含中文
SELECT DISTINCT(LicenseNo) FROM vehicle a WHERE 1 = 1 AND ((SELECT COUNT(LicenseNo) FROM vehicle WHERE LicenseNo = a.LicenseNo) > 1) ;
4.适用于字元串類型,不包含中文
SELECT DISTINCT (a.CarVIN) FROM vehicle a LEFT JOIN vehicle b ON a.CarVIN=b.CarVIN WHERE 1=1 AND a.id<>b.Id;
轉載 https://mp.weixin.qq.com/s/U5nZ0Ss_oJ3W1CgF3SvtBQ