PostgreSQL COLLATE用來設定欄位的排序規則及字元分類，又稱為「定序」。
資料庫執行ORDER BY敘述時會依照欄位值將資料做排序，而資料庫的collation則決定欄位的排序規則，例如英文是否區分大小寫、中文是用筆畫還是注音排序等。
執行SELECT * FROM pg_collation或在psql輸入/dOS+可查詢PostgreSQL預先定義的collation表。
postgres=> \dOS+
List of collations
Schema | Name | Collate | Ctype | Provider | Deterministic? | Description
------------+------------------------+------------------+------------------+----------+----------------+----------------------------------------------
pg_catalog | C | C | C | libc | yes | standard C collation
pg_catalog | POSIX | POSIX | POSIX | libc | yes | standard POSIX collation
...
pg_catalog | zh-Hans-CN-x-icu | zh-Hans-CN | zh-Hans-CN | icu | yes | Chinese (Simplified, China)
pg_catalog | zh-Hans-HK-x-icu | zh-Hans-HK | zh-Hans-HK | icu | yes | Chinese (Simplified, Hong Kong SAR China)
pg_catalog | zh-Hans-MO-x-icu | zh-Hans-MO | zh-Hans-MO | icu | yes | Chinese (Simplified, Macao SAR China)
pg_catalog | zh-Hans-SG-x-icu | zh-Hans-SG | zh-Hans-SG | icu | yes | Chinese (Simplified, Singapore)
pg_catalog | zh-Hans-x-icu | zh-Hans | zh-Hans | icu | yes | Chinese (Simplified)
pg_catalog | zh-Hant-HK-x-icu | zh-Hant-HK | zh-Hant-HK | icu | yes | Chinese (Traditional, Hong Kong SAR China)
pg_catalog | zh-Hant-MO-x-icu | zh-Hant-MO | zh-Hant-MO | icu | yes | Chinese (Traditional, Macao SAR China)
pg_catalog | zh-Hant-TW-x-icu | zh-Hant-TW | zh-Hant-TW | icu | yes | Chinese (Traditional, Taiwan)
pg_catalog | zh-Hant-x-icu | zh-Hant | zh-Hant | icu | yes | Chinese (Traditional)
pg_catalog | zh-x-icu | zh | zh | icu | yes | Chinese
pg_catalog | zh_CN | zh_CN | zh_CN | libc | yes |
pg_catalog | zh_CN.UTF-8 | zh_CN.UTF-8 | zh_CN.UTF-8 | libc | yes |
pg_catalog | zh_HK | zh_HK | zh_HK | libc | yes |
pg_catalog | zh_HK.UTF-8 | zh_HK.UTF-8 | zh_HK.UTF-8 | libc | yes |
pg_catalog | zh_TW | zh_TW | zh_TW | libc | yes |
pg_catalog | zh_TW.UTF-8 | zh_TW.UTF-8 | zh_TW.UTF-8 | libc | yes |
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