我有一个varchar列的表,我想找到在这个列中有重复值的所有记录。我可以使用什么查询来查找重复项?
当前回答
下面的代码将找到所有使用了不止一次的product_id。每个product_id只能得到一条记录。
SELECT product_id FROM oc_product_reward GROUP BY product_id HAVING count( product_id ) >1
代码取自:http://chandreshrana.blogspot.in/2014/12/find-duplicate-records-based-on-any.html
其他回答
如果要删除具有多个字段的重复行,首先将它们取消为唯一不同的行指定的新唯一键,然后使用group by命令删除具有相同新唯一键的重复行:
Create TEMPORARY table tmp select concat(f1,f2) as cfs,t1.* from mytable as t1;
Create index x_tmp_cfs on tmp(cfs);
Create table unduptable select f1,f2,... from tmp group by cfs;
SELECT ColumnA, COUNT( * )
FROM Table
GROUP BY ColumnA
HAVING COUNT( * ) > 1
我更喜欢使用窗口函数(MySQL 8.0+)来查找副本,因为我可以看到整行:
WITH cte AS (
SELECT *
,COUNT(*) OVER(PARTITION BY col_name) AS num_of_duplicates_group
,ROW_NUMBER() OVER(PARTITION BY col_name ORDER BY col_name2) AS pos_in_group
FROM table
)
SELECT *
FROM cte
WHERE num_of_duplicates_group > 1;
DB小提琴演示
SELECT DISTINCT a.email FROM `users` a LEFT JOIN `users` b ON a.email = b.email WHERE a.id != b.id;
根据levik的回答来获取重复行的id,如果服务器支持的话,可以执行GROUP_CONCAT(这将返回一个以逗号分隔的id列表)。
SELECT GROUP_CONCAT(id), name, COUNT(*) c
FROM documents
GROUP BY name
HAVING c > 1;