And that’s how we can delete duplicate records in SQL Server with tables without primary key, containing primary key and by keeping one original row. 原文链接:http://www.codesec.net/view/449563.html
All rows in Oracle have a rowid. This is a physical locator. That is, it states where on disk Oracle stores the row. This unique to each row. So you can use this value to identify and remove copies. To do this, replace min() with min(rowid) in the uncorrelated delete: Copy code ...
TheROW_NUMBER()function returns the sequential number for each row within the previously defined partition. Like theCOUNT()function, it can find duplicates in the table. Below is the syntax for this action: SELECT *, ROW_NUMBER() OVER (PARTITION BY [column1],[column2],[column3] ORDER BY...
The only reason to spend time doing logic on the source query is if it will result in a total reduced load on the OLTP. e.g. Incremental logic on a 10million row table may result in a faster query and shorter locks than if you try and do a dumb load of 10million rows every ...
We use the SQLMAXfunction to calculate the max id of each data row. 1 2 3 4 5 6 7 8 9 10 SELECT* FROM[SampleDB].[dbo].[Employee] WHEREIDNOTIN ( SELECTMAX(ID) FROM[SampleDB].[dbo].[Employee] GROUPBY[FirstName], [LastName], ...
mysql tables in use 1, locked 1 LOCK WAIT 3 lock struct(s), heap size 1136, 2 row lock(s), undo log entries 1 MySQL thread id 23, OS thread handle 14896, query id 582 localhost ::1 root update insert into song_rank(songId,weight) values(18,100) on duplicate key update weight=...
SQL>alterdatabase force logging; Database altered. 取消强制日志模式如下: SQL>alterdatabasenoforce logging; Database altered. 2)其次,检查主数据库的日志运行模式,Data Guard要求主数据库必须在归档模式下运行,此模式下数据库可以连续完整的保存事务日志。
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If a=1 OR b=2 matches several rows, only one row is updated. In general, you should try to avoid using an ON DUPLICATE KEY UPDATE clause on tables with multiple unique indexes. 接下来实验一下,给 t1 加的 b 也加上唯一索引: ALTER TA...
逻辑上我们需要怎么写: result = mysql_query(‘select * from xxx where id = 1’);row = mysql_fetch_assoc( 但是这样写有两个问题...1、效率太差,每次执行都要执行2个sql 2、高并发的情况下数据会出问题,不能保证原子性 还好MySQL 为我们解决了这个问题:我们可以通过 ON DUPLICATE KEY UPDATE 达到以上...