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SQL优化[23]

[入库：2005年8月18日] [更新：2007年3月24日]

本文简介：选择自 fly_miss 的 blog
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9、字段提取要按照“需多少、提多少”的原则，避免“select *”

我们来做一个试验：

select top 10000 gid,fariqi,reader,title from tgongwen order by gid desc

用时：4673毫秒

select top 10000 gid,fariqi,title from tgongwen order by gid desc

用时：1376毫秒

select top 10000 gid,fariqi from tgongwen order by gid desc

用时：80毫秒

由此看来，我们每少提取一个字段，数据的提取速度就会有相应的提升。提升的速度还要看您舍弃的字段的大小来判断。

10、count(*)不比count(字段)慢

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