Question

^{（原来是this question的一部分，但它有点无关紧要，所以我决定把它作为自己的问题。）}

我找不到运算符~<~。 Postgres手册仅提及~和类似操作符here，但没有~<~的迹象。

当在psql控制台中摆弄时，我发现这些命令会产生相同的结果：

SELECT * FROM test ORDER BY name USING ~<~;
SELECT * FROM test ORDER BY name COLLATE "C";

这些给出了反向排序：

SELECT * FROM test ORDER BY name USING ~>~;
SELECT * FROM test ORDER BY name COLLATE "C" DESC;

还有关于代字号运算符的一些信息：

\do ~*~
                                    List of operators
  Schema   | Name | Left arg type | Right arg type | Result type |       Description       
------------+------+---------------+----------------+-------------+-------------------------
pg_catalog | ~<=~ | character     | character      | boolean     | less than or equal
pg_catalog | ~<=~ | text          | text           | boolean     | less than or equal
pg_catalog | ~<~  | character     | character      | boolean     | less than
pg_catalog | ~<~  | text          | text           | boolean     | less than
pg_catalog | ~>=~ | character     | character      | boolean     | greater than or equal
pg_catalog | ~>=~ | text          | text           | boolean     | greater than or equal
pg_catalog | ~>~  | character     | character      | boolean     | greater than
pg_catalog | ~>~  | text          | text           | boolean     | greater than
pg_catalog | ~~   | bytea         | bytea          | boolean     | matches LIKE expression
pg_catalog | ~~   | character     | text           | boolean     | matches LIKE expression
pg_catalog | ~~   | name          | text           | boolean     | matches LIKE expression
pg_catalog | ~~   | text          | text           | boolean     | matches LIKE expression
(12 rows)

第3行和第4行是我正在寻找的运算符，但描述对我来说有点不足。

Answer 1

~>=~，~<=~，~>~和~<~是text模式（或varchar，基本相同）运算符，对应的他们各自的兄弟姐妹>=，<=，>和<。他们严格按字节值对字符数据进行排序，忽略任何整理设置的规则（与其兄弟姐妹相对）。这使得它们更快，但对大多数语言/国家也无效。

“C”语言环境实际上与 no locale 相同，这意味着没有整理规则。这解释了为什么ORDER BY name USING ~<~和ORDER BY name COLLATE "C"最终会做同样的事情。

关于dba.SE的相关答案的最后一章的详细解释：

Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL

请注意， ~~ 是用于实现SQL LIKE expression的Postgres运算符，与几乎不相关。同样，~~*实现ILIKE。更多：

~~ Operator In Postgres

Symfony2 Doctrine - ILIKE clause for PostgreSQL?

PostgreSQL - text Array contains value similar to

运营商〜＆lt;〜在Postgres

1 个答案: