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
SELECT
t.*,
(SELECT COUNT(*) FROM city AS tt WHERE tt.name=t.name) AS count
FROM `city` AS t
WHERE
(SELECT count(*) FROM city AS tt WHERE tt.name=t.name) > 1 ORDER BY count DESC
其他回答
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
对GROUP BY子句执行SELECT操作。假设name是你想要在其中找到重复项的列:
SELECT name, COUNT(*) c FROM table GROUP BY name HAVING c > 1;
这将返回一个在第一列中包含名称值的结果,以及该值在第二列中出现次数的计数。
我看到上面的结果和查询将工作良好,如果你需要检查单列值是重复的。比如电子邮件。
但如果你需要检查更多的列,并希望检查结果的组合,那么这个查询将正常工作:
SELECT COUNT(CONCAT(name,email)) AS tot,
name,
email
FROM users
GROUP BY CONCAT(name,email)
HAVING tot>1 (This query will SHOW the USER list which ARE greater THAN 1
AND also COUNT)
感谢@novocaine的精彩回答,他的解决方案对我很有效。我稍微改变了它,以包括一个百分比的循环值,这在我的例子中是需要的。以下是修改后的版本。它将百分比减少到小数点后两位。如果你把2改成0,它就不会显示小数,改成1,它就会显示一位小数,以此类推。
SELECT GROUP_CONCAT(id), name, COUNT(*) c,
COUNT(*) OVER() AS totalRecords,
CONCAT(FORMAT(COUNT(*)/COUNT(*) OVER()*100,2),'%') as recurringPecentage
FROM table
GROUP BY name
HAVING c > 1
CREATE TABLE tbl_master
(`id` int, `email` varchar(15));
INSERT INTO tbl_master
(`id`, `email`) VALUES
(1, 'test1@gmail.com'),
(2, 'test2@gmail.com'),
(3, 'test1@gmail.com'),
(4, 'test2@gmail.com'),
(5, 'test5@gmail.com');
QUERY : SELECT id, email FROM tbl_master
WHERE email IN (SELECT email FROM tbl_master GROUP BY email HAVING COUNT(id) > 1)