相当于 MySQL 中 Oracle 的 RowID
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Equivalent of Oracle’s RowID in MySQL
提问by raj
is there an equivalent of oracle's rowid in mysql?
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)
delete from my_table where rowid not in (select max(rowid) from my_table group by field1,field2)
I want to make a mysql equivalent of this query!!!
我想制作一个相当于这个查询的 mysql ！！！
What i'm trying to do is, : The my_table has no primary key.. i'm trying to delete the duplicate values and impose a primary key (composite of field1, field2)..!!
我想要做的是： my_table 没有主键.. 我正在尝试删除重复值并强加一个主键（field1、field2 的组合）..!!
回答by newtover
In MySql you usually use session variables to achive the functionality:
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
But you can not make sorts on the table you are trying to delete from in subqueries.
但是您无法在子查询中对要从中删除的表进行排序。
UPD: that is you will need to create a temp table, insert the ranging subquery to the temp table and delete from the original table by joining with the temporary table (you will need some unique row identifier):
UPD：也就是说，您需要创建一个临时表，将范围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
Since that is one time operation, this should not bring too much overhead.
由于这是一次操作，因此不应带来太多开销。
回答by Alexey Gerasimov
Maybe, I am misreading the question but your query (even in Oracle) doesn't accomplish your desired goal:
也许，我误读了这个问题，但您的查询（即使在 Oracle 中）也没有实现您想要的目标：
delete from my_table where rowid not in (select max(rowid) from
my_table group by field1,field2)
MySQL equivalent is
MySQL等价物是
SELECT @rowid:=max(rowid) from my_table;
DELETE FROM my_table where rowid != @rowid;
This will wipe out all rows except for last one.
这将清除除最后一行之外的所有行。
To perform one time cleanup (removing duplicate records) of your data you can do this:
要对数据执行一次性清理（删除重复记录），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;
Then add whatever columns & keys necessary by ALTER TABLE. Above code might require to drop any foreign keys you might have.
然后添加 ALTER TABLE 所需的任何列和键。上面的代码可能需要删除您可能拥有的任何外键。
回答by Mukesh Kumar
mysql> set @row_num = 0;
First set rowId or row num the use it as following:
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;
回答by mosheb
you can avoid the temp table using another derived table:
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
