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)

我想创建一个与此查询等效的mysql！

我正在尝试做的是：my_table没有主键..我正在尝试删除重复值并强加主键（field1，field2的组合）.. !!

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

但是你不能在你试图从子查询中删除的表上进行排序。

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。

Answer 2

也许，我误解了这个问题，但你的查询（即使在Oracle中）并没有达到你想要的目标：

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

MySQL等价物是

SELECT @rowid:=max(rowid) from my_table;
DELETE FROP my_table where rowid != @rowid;

这将消除除最后一行之外的所有行。

要执行一次清理（删除重复记录）数据，您可以执行以下操作：

CREATE TABLE my_table2 SELECT distinct f1, f2, f3, etc from my_table;
DROP TABLE my_table;
ALTER TABLE my_table2 RENAME my_table;

然后添加任何列和＆amp; ALTER TABLE所需的密钥。上面的代码可能需要删除你可能拥有的任何外键。

Answer 3

您可以使用另一个派生表来避免临时表：

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

Answer 4

mysql> set @row_num = 0;

首先设置rowId或row num，使用它如下：

mysql>  SELECT @row_num := @row_num + 1 as row_number,id,name,salary FROM employee
ORDER BY salary;

相当于MySQL中的Oracle RowID

4 个答案: