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Update ddl.sgml #451

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Update ddl.sgml #451

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2 changes: 1 addition & 1 deletion postgresql/doc/src/sgml/ddl.sgml
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Expand Up @@ -4733,7 +4733,7 @@ EXPLAIN SELECT count(*) FROM measurement WHERE logdate >= DATE '2008-01-01';
-->
<para>
请注意，约束排除只由<literal>CHECK</>约束驱动，而不会由索引驱动。
因此，在关键字字段上定义索引是没有必要的。
因此，在关键字字段上定义索引是非必要的。
在给出的分区上是否需要建立索引取决于那些扫描该分区的查询通常是扫描该分区的一大部分还是只是一小部分。
对于后者，索引通常都有帮助，对于前者则没有什么好处。
</para>
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