如何从MySQL表中删除重复的行

I have a MySQL table like:

我有一个MySQL表,如:

ID, Col1, Col2, Col3, Col4, etc...

ID is a primary key and has been working since the table's creation.

ID是主键,自表创建以来一直在工作。

What I want to do is delete all but one records where all the other columns are identical.

我想要做的是删除除一条记录之外的所有其他列相同的记录。

8 个解决方案

#1

DELETE DupRows.*
FROM MyTable AS DupRows
   INNER JOIN (
      SELECT MIN(ID) AS minId, col1, col2
      FROM MyTable
      GROUP BY col1, col2
      HAVING COUNT(*) > 1
   ) AS SaveRows ON SaveRows.col1 = DupRows.col1 AND SaveRows.col2 = DupRows.col2
      AND SaveRows.minId <> DupRows.ID;

Of course you have to extend col1, col2 in all three places to all columns.

当然,您必须将所有三个位置的col1,col2扩展到所有列。

Edit: I just pulled this out of a script I keep and re-tested, it executes in MySQL.

编辑:我刚刚从我保留并重新测试的脚本中取出它,它在MySQL中执行。

#2

RENAME TABLE [table w/ duplicates] TO [temporary table name]

RENAME TABLE [table w / duplicatelicates] TO [临时表名]
Create an identical table with the original table name which contained the duplicates.

使用包含重复项的原始表名创建相同的表。
INSERT INTO [new table] SELECT DISTINCT * FROM [old table with duplicates]

INSERT INTO [新表] SELECT DISTINCT * FROM [带有重复项的旧表]
Delete the temporary tables.

删除临时表。

#3

Without nested selects or temporary tables.

没有嵌套的选择或临时表。

DELETE  t1
FROM    table_name t1, table_name t2
WHERE   
            (t1.Col1 = t2.Col1 OR t1.Col1 IS NULL AND t2.Col1 IS NULL)
        AND (t1.Col2 = t2.Col2 OR t1.Col2 IS NULL AND t2.Col2 IS NULL)
        AND (t1.Col3 = t2.Col3 OR t1.Col3 IS NULL AND t2.Col3 IS NULL)
        AND (t1.Col4 = t2.Col4 OR t1.Col4 IS NULL AND t2.Col4 IS NULL)
        ...
        AND t1.ID < t2.ID;

#4

I'd do it following way, in MSSQL, but I think it should work with slight modifications in MySQL. Not executable, but should show the way.

我会在MSSQL中按照以下方式执行此操作,但我认为它应该可以在MySQL中稍作修改。不可执行,但应该显示方式。

CREATE TEMPORARY TABLE #Table (Col1, Col2, Col3);
INSERT INTO #Table (Col1, Col2, Col3) SELECT DISTINCT Col1, Col2, Col3 FROM Table;
DELETE FROM Table;
INSERT INTO Table (Col1, Col2, Col3) SELECT Col1, Col2, Col3 FROM #Table;
DROP TABLE #Table;

#5

you can also do this

你也可以这样做

Create table new_table{id, col1,col2,col3}

insert into new_table values(select distinct * from old_table)

drop table old_table

#6

you can delete all the rows except one by using some function like Min(depends on db). Ex:

你可以使用像Min这样的函数删除除一个之外的所有行(取决于db)。例如:

delete from Table_Name
where Id not in
( select min(Id)
from  Table_Name
group by ID, Col1, Col2, Col3, Col4);

#7

You can try this with the help of join : Like that way:

你可以在join的帮助下尝试这个:就像这样:

DELETE e1 FROM emp_tbl AS e1 JOIN emp_tbl AS e2 WHERE 
e1.Col1=e2.Col1 AND e1.Col2=e2.Col2 AND e1.Col3=e2.Col3 AND e1.Col4=e2.Col4
AND e1.id < e2.id;

#8

You can run an alter query and achieve this:

您可以运行alter query并实现此目的:

ALTER IGNORE TABLE tbl_1
ADD UNIQUE INDEX unq_idx(col1, col2, col3);

I cant guarantee it will retain the first record among the duplicates, but MySQL usually does that.

我不能保证它会保留重复项中的第一条记录,但MySQL通常会这样做。

#1

DELETE DupRows.*
FROM MyTable AS DupRows
   INNER JOIN (
      SELECT MIN(ID) AS minId, col1, col2
      FROM MyTable
      GROUP BY col1, col2
      HAVING COUNT(*) > 1
   ) AS SaveRows ON SaveRows.col1 = DupRows.col1 AND SaveRows.col2 = DupRows.col2
      AND SaveRows.minId <> DupRows.ID;