mysql UPDATE语句-对于相同值的开销? [英] mysql UPDATE statement - overhead for same values?

问题描述

我有一个拥有成千上万条记录的大型MYSQL数据库.我想更新其中的一个字段，但我不知道该字段是否已更新.

如果我调用一个将authortype = 10设置为authortype且已将authortype设置为10的更新语句，这会比执行单独的查询来仅选择不是authortype = 10的查询然后更新它们的速度更快吗?

换句话说，如果我将值设置为已经等于的值，这是否比我将值更新为新值快?再次有无数的记录，我想提高效率.

预先感谢

解决方案

为什么不只是使用

UPDATE  dbo.Authors
SET     AuthorType = 10
WHERE   AuthorType <> 10

并且两全其美.

请注意，对于任何现代数据库引擎而言，数十万条记录都不会造成任何问题.

次要编辑

i have a large MYSQL database with hundreds of thousands of records. i want to update a field in a large number of them, but I am unaware if that field has been updated yet or not.

if i call an update statement that sets authortype=10 and authortype is already 10 will this be faster than doing a separate query to only select those that aren't authortype=10 and then update them?

in other words, if I set a value equal to what it is already, is that any faster than if I am updating a value to something new? again this is with tons and tons of records and I want to be efficient.

thanks in advance

解决方案

Why not just use

UPDATE  dbo.Authors
SET     AuthorType = 10
WHERE   AuthorType <> 10

and have the best of both worlds.

Note that a few hundred thousands records should pose no problem for any modern database engine.

Minor edit

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