如何删除没有唯一行id存在的重复行?
我的座位是
col1 col2 col3 col4 col5 col6 col7
john 1 1 1 1 1 1
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
sally 2 2 2 2 2 2
我想留下以下重复删除后:
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
我尝试了一些查询，但我认为他们取决于有一个行id，因为我没有得到想要的结果。例如:
DELETE
FROM table
WHERE col1 IN (
SELECT id
FROM table
GROUP BY id
HAVING (COUNT(col1) > 1)
)
当前回答
在mysql中有两个解决方案:
A)使用Delete JOIN语句删除重复的行
DELETE t1 FROM contacts t1
INNER JOIN contacts t2
WHERE
t1.id < t2.id AND
t1.email = t2.email;
该查询两次引用联系人表，因此，它使用表别名t1和t2。
输出结果为:
1 查询确定，影响4行(0.10秒)
如果你想删除重复的行并保留最低的id，你可以使用下面的语句:
DELETE c1 FROM contacts c1
INNER JOIN contacts c2
WHERE
c1.id > c2.id AND
c1.email = c2.email;
B)使用中间表删除重复的行
下面是使用中间表删除重复行的步骤:
1。创建一个新表，其结构与要删除重复行的原始表相同。
2。将原始表中的不同行插入到直接表中。
3所示。将原始表中的不同行插入到直接表中。
步骤1。创建一个与原表结构相同的新表:
CREATE TABLE source_copy LIKE source;
步骤2。从原表中插入不同的行到新表中:
INSERT INTO source_copy
SELECT * FROM source
GROUP BY col; -- column that has duplicate values
步骤3。删除原始表并将直接表重命名为原始表
DROP TABLE source;
ALTER TABLE source_copy RENAME TO source;
来源:http://www.mysqltutorial.org/mysql-delete-duplicate-rows/
其他回答
-- this query will keep only one instance of a duplicate record.
;WITH cte
AS (SELECT ROW_NUMBER() OVER (PARTITION BY col1, col2, col3-- based on what? --can be multiple columns
ORDER BY ( SELECT 0)) RN
FROM Mytable)
delete FROM cte
WHERE RN > 1
这可能对你的情况有帮助
DELETE t1 FROM table t1 INNER JOIN table t2 WHERE t1.id > t2.id AND t1.col1 = t2.col1
哦，哇，我觉得准备这些答案太愚蠢了，他们就像专家的答案，包括所有的CTE和临时表等。
为了让它工作，我所做的只是使用MAX聚合ID列。
DELETE FROM table WHERE col1 IN (
SELECT MAX(id) FROM table GROUP BY id HAVING ( COUNT(col1) > 1 )
)
注意:您可能需要多次运行它来删除重复，因为这一次只会删除一组重复的行。
DELETE p1 FROM Person p1,
Person p2
WHERE
p1.Email = p2.Email AND p1.Id > p2.Id
DECLARE @TB TABLE(NAME VARCHAR(100));
INSERT INTO @TB VALUES ('Red'),('Red'),('Green'),('Blue'),('White'),('White')
--**Delete by Rank**
;WITH CTE AS(SELECT NAME,DENSE_RANK() OVER (PARTITION BY NAME ORDER BY NEWID()) ID FROM @TB)
DELETE FROM CTE WHERE ID>1
SELECT NAME FROM @TB;
--**Delete by Row Number**
;WITH CTE AS(SELECT NAME,ROW_NUMBER() OVER (PARTITION BY NAME ORDER BY NAME) ID FROM @TB)
DELETE FROM CTE WHERE ID>1;
SELECT NAME FROM @TB;
