Question

我有一个MySQL表，如：

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

ID是 primary key ，自该表创建以来一直在运作。

我想要做的是删除所有其他列完全相同的所有记录。

Answer 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;

当然，你必须将所有三个地方的col1，col2扩展到所有列。

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。

Answer 2

RENAME TABLE [table w/ duplicates] TO [temporary table name]
使用包含重复项的原始表名创建一个相同的表。
INSERT INTO [new table] SELECT DISTINCT * FROM [old table with duplicates]
删除临时表。

Answer 3

没有嵌套选择或临时表。

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;

Answer 4

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;

Answer 5

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

Answer 6

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);

Answer 7

您可以在加入的帮助下尝试此操作：就像那样：

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;

Answer 8

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);

我无法保证它会保留重复项中的第一条记录，但MySQL通常会这样做。

如何从MySQL表中删除重复的行

8 个答案: