MySQL查詢表中某個字段的重復數據

1. 查詢SQL表中某個字段的重復數據

SELECT user_name,COUNT(*) AS count FROM db_user_info GROUP BY user_name HAVING count > 1;

SELECT user_name FROM db_user_info GROUP BY user_name HAVING COUNT(1) > 1;

SELECT * FROM db_user_info WHERE user_name IN (SELECT user_name FROM db_user_info GROUP BY user_name HAVING COUNT(1) > 1);

• HAVING是分組（GROUP BY）后的篩選條件，分組后的數據組內再篩選；WHERE 則是在分組前篩選。
• WHERE 子句中不能使用聚集函數，而 HAVING 子句中可以，所以在集合函數中加上了 HAVING 來起到測試查詢結果是否符合條件的作用。即 HAVING 子句的適用場景是可以使用聚合函數。