SQL常用语句之-查询数据库表中的字段上的重复数据

--查询数据库表中的某个字段数据是否有重复.
--方法一
SELECT id2, COUNT(*) AS 重复数据 FROM table_1 GROUP BY id2 HAVING COUNT(*)>=2
--方法二
SELECT table_1.* FROM table_1
RIGHT JOIN(SELECT ID2 FROM table_1 GROUP BY ID2 HAVING COUNT(ID2)>1)
T ON table_1.ID2=T.ID2
--查询数据库表中某两个字段数据是否有重复
SELECT Table_1.* FROM table_1
RIGHT JOIN( SELECT ID2,ID3 FROM table_1 GROUP BY ID2,ID3 HAVING COUNT(ID2)>1 AND COUNT(ID3)>1)
T ON T.ID2=table_1.ID2 AND T.ID3=table_1.ID3

--方法三

SELECT tb1.* FROM tb1
RIGHT JOIN(SELECT 现表, 现字段 FROM tb1 GROUP BY 现表, 现字段 HAVING COUNT(现字段)>1)
T ON tb1.现字段=T.现字段 and tb1.现表=T.现表