pgsql locale影响说明

最新推荐文章于 2024-05-27 09:44:59 发布

国强余富

最新推荐文章于 2024-05-27 09:44:59 发布

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本文探讨了 PostgreSQL 数据库中 locale 设置如何影响 SQL 功能，如排序、大小写转换、模式匹配以及 to_char 函数等。使用非 C 或 POSIX locale 虽然提供了特定语言环境的功能，但会降低性能并阻止某些索引的使用。为解决这个问题，可以利用定制的 operator classes 创建忽略 locale 规则的索引，或者使用 C collation 的索引。在决定使用 locale 时，应谨慎权衡其带来的性能影响和实际需求。

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The locale settings influence the following SQL features:

Sort order in queries using ORDER BY or the standard comparison operators on textual data
The upper, lower, and initcap functions
Pattern matching operators (LIKE, SIMILAR TO, and POSIX-style regular expressions); locales affect both case insensitive matching and the classification of characters by character-class regular expressions
The to_char family of functions
The ability to use indexes with LIKE clauses

The drawback of using locales other than C or POSIX in PostgreSQL is its performance impact. It slows character handling and prevents ordinary indexes from being used by LIKE. For this reason use locales only if you actually need them.

As a workaround to allow PostgreSQL to use indexes with LIKE clauses under a non-C locale, several custom operator classes exist. These allow the creation of an index that performs a strict character-by-character comparison, ignoring locale comparison rules. Refer to Section 11.10 for more information. Another approach is to create indexes using the C collation, as discussed in Section 23.2.