Question

我有一个包含varchar列的表，我想在此列中找到所有具有重复值的记录。我可以用什么来查找重复的最佳查询？

Answer 1

使用SELECT条款执行GROUP BY。假设 name 是您要在其中找到重复项的列：

SELECT name, COUNT(*) c FROM table GROUP BY name HAVING c > 1;

这将返回第一列中 name 值的结果，以及该值在第二列中出现的次数。

Answer 2

SELECT varchar_col
FROM table
GROUP BY varchar_col
HAVING COUNT(*) > 1;

Answer 3

SELECT  *
FROM    mytable mto
WHERE   EXISTS
        (
        SELECT  1
        FROM    mytable mti
        WHERE   mti.varchar_column = mto.varchar_column
        LIMIT 1, 1
        )

此查询返回完整记录，而不仅仅是不同的varchar_column。

此查询不使用COUNT(*)。如果有很多重复项，COUNT(*)代价很高，并且您不需要整个COUNT(*)，则只需要知道是否有两行具有相同的值。

在varchar_column上建立索引当然会大大加快此查询的速度。

Answer 4

根据levik的答案来获取重复行的ID，如果你的服务器支持它，你可以做GROUP_CONCAT（这将返回逗号分隔的id列表）。

SELECT GROUP_CONCAT(id), name, COUNT(*) c FROM documents GROUP BY name HAVING c > 1;

Answer 5

SELECT * 
FROM `dps` 
WHERE pid IN (SELECT pid FROM `dps` GROUP BY pid HAVING COUNT(pid)>1)

Answer 6

假设您的表名为TableABC，而您想要的列是Col，而T1的主键是Key。

SELECT a.Key, b.Key, a.Col 
FROM TableABC a, TableABC b
WHERE a.Col = b.Col 
AND a.Key <> b.Key

这种方法优于上述答案的优势在于它提供了密钥。

Answer 7

要查找Employee中名称列中有多少记录重复，下面的查询会很有用;

Select name from employee group by name having count(*)>1;

Answer 8

我没有看到任何JOIN方法，它们在重复方面有很多用途。

这种方法可以为您提供实际的双倍结果。

SELECT t1.* FROM my_table as t1 
LEFT JOIN my_table as t2 
ON t1.name=t2.name and t1.id!=t2.id 
WHERE t2.id IS NOT NULL 
ORDER BY t1.name

Answer 9

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

将城市替换为您的表格。将名称替换为您的字段名称

Answer 10

我的最后一个问题包含了一些有用的答案 - 将group by，count＆amp; GROUP_CONCAT。

SELECT GROUP_CONCAT(id), `magento_simple`, COUNT(*) c 
FROM product_variant 
GROUP BY `magento_simple` HAVING c > 1;

这提供了两个示例（逗号分隔）的ID，我需要的条形码以及重复的数量。

相应地更改表格和列。

Answer 11

如果您需要检查重复的单列值，我看到上面的结果和查询将正常工作。例如电子邮件。

但是如果您需要检查更多列并想检查结果的组合，那么此查询将正常工作：

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)

Answer 12

进一步@maxyfc's answer，我需要找到带有重复值的所有行，因此我可以在MySQL Workbench中对其进行编辑：

const auth_url = "/connect/facebook";
<form className="signin__form" action={auth_url} method="post">
    <input type="hidden" name="scope" value="user_friends" />
    <button type="submit" className="signin__form-btn">
    SIGN IN WITH FACEBOOK
    </button>
</form>

Answer 13

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)

Answer 14

以下内容将查找多次使用的所有product_id。您只能获得每个product_id的单个记录。

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

Answer 15

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

Answer 16

SELECT DISTINCT a.email FROM `users` a LEFT JOIN `users` b ON a.email = b.email WHERE a.id != b.id;

Answer 17

我更喜欢使用窗口函数（MySQL 8.0+）查找重复项，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 Fiddle Demo

Answer 18

要删除包含多个字段的重复行，首先将它们设置为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;

Answer 19

Select column_name, column_name1,column_name2, count(1) as temp from table_name group by column_name having temp > 1

Answer 20

一个非常晚的贡献......万一它可以帮助任何人下线...我有一个任务是在银行应用中找到匹配的交易对（实际上是账户到账户转账的两面），到确定哪些是＆＃39;来自＆＃39;和＆＃39;到＆＃39;对于每个账户间转账交易，我们最终得到了这个：

SELECT 
    LEAST(primaryid, secondaryid) AS transactionid1,
    GREATEST(primaryid, secondaryid) AS transactionid2
FROM (
    SELECT table1.transactionid AS primaryid, 
        table2.transactionid AS secondaryid
    FROM financial_transactions table1
    INNER JOIN financial_transactions table2 
    ON table1.accountid = table2.accountid
    AND table1.transactionid <> table2.transactionid 
    AND table1.transactiondate = table2.transactiondate
    AND table1.sourceref = table2.destinationref
    AND table1.amount = (0 - table2.amount)
) AS DuplicateResultsTable
GROUP BY transactionid1
ORDER BY transactionid1;

结果是DuplicateResultsTable提供了包含匹配（即重复）事务的行，但它在第二次匹配同一对时也提供了相同的事务ID，因此外部{ {1}}可以按第一个交易ID进行分组，使用SELECT和LEAST来确保两个交易代码在结果中始终保持相同的顺序，这使得第一个GREATEST安全，从而消除了所有重复的匹配。超过近百万条记录，并在不到2秒的时间内确定了12,000多场比赛。当然，transactionid是主要索引，这确实有帮助。

Answer 21

SELECT ColumnA, COUNT( * )
FROM Table
GROUP BY ColumnA
HAVING COUNT( * ) > 1

Answer 22

如果要删除重复项，请使用DISTINCT

否则使用此查询：

SELECT users.*,COUNT(user_ID) as user FROM users GROUP BY user_name HAVING user > 1;

Answer 23

作为 Levik 答案的一个变体，它允许您同时找到重复结果的 id，我使用了以下内容：

SELECT * FROM table1 WHERE column1 IN (SELECT column1 AS duplicate_value FROM table1 GROUP BY column1 HAVING COUNT(*) > 1)

Answer 24

尝试使用此查询：

SELECT name, COUNT(*) value_count FROM company_master GROUP BY name HAVING value_count > 1;

Answer 25

要获取所有包含重复项的数据，我使用了以下方法：

SELECT * FROM TableName INNER JOIN(
  SELECT DupliactedData FROM TableName GROUP BY DupliactedData HAVING COUNT(DupliactedData) > 1 order by DupliactedData)
  temp ON TableName.DupliactedData = temp.DupliactedData;

TableName =您正在使用的表。

DupliactedData =您要查找的重复数据。

Answer 26

我对此有所改进：

SELECT 
    col, 
    COUNT(col)
FROM
    table_name
GROUP BY col
HAVING COUNT(col) > 1;

在MySQL中查找重复值

26 个答案: