相当于MySQL中的Oracle RowID

Question

在mysql中是否有相当于oracle的rowid？

delete from my_table where rowid not in (select max(rowid) from my_table group by field1,field2)

我想制作一个相当于这个查询的mysql!

我要做的是,:my_table没有主键..我正在尝试删除重复的值并强加一个主键(field1,field2的复合).. !!

Answer 1

在MySql中,您通常使用会话变量来实现功能:

SELECT @rowid:=@rowid+1 as rowid
FROM table1, (SELECT @rowid:=0) as init
ORDER BY sorter_field

但是您无法对要从子查询中删除的表进行排序.

UPD:您需要创建临时表,将测距子查询插入临时表,并通过连接临时表从原始表中删除(您将需要一些唯一的行标识符):

CREATE TEMPORARY TABLE duplicates ...

INSERT INTO duplicates (rowid, field1, field2, some_row_uid)
SELECT
  @rowid:=IF(@f1=field1 AND @f2=field2, @rowid+1, 0) as rowid,
  @f1:=field1 as field1,
  @f2:=field2 as field2,
  some_row_uid
FROM testruns t, (SELECT @rowid:=NULL, @f1:=NULL, @f2:=NULL) as init
ORDER BY field1, field2 DESC;

DELETE FROM my_table USING my_table JOIN duplicates
  ON my_table.some_row_uid = duplicates.some_row_uid AND duplicates.rowid > 0

由于这是一次性操作,因此不应带来太多开销.