PostgreSQL 语法

默认情况下 PostgreSQL 安装完成后，自带了一个命令行工具 SQL Shell(psql)。

Linux 系统可以直接切换到 postgres 用户来开启命令行工具：

#  sudo -i -u postgres

Windows 系统一般在它的安装目录下：

Program Files → PostgreSQL 11.3 → SQL Shell(psql)

Mac OS 我们直接搜索就可以了找到：

进入命令行工具，我们可以使用 \help 来查看各个命令的语法：

postgres-# \help <command_name>

例如，我们查看下 select 语句的语法：

postgres=# \help SELECT
Command:     SELECT
Description: retrieve rows from a table or view
Syntax:
[ WITH [ RECURSIVE ] with_query [, ...] ]
SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
    [ * | expression [ [ AS ] output_name ] [, ...] ]
    [ FROM from_item [, ...] ]
    [ WHERE condition ]
    [ GROUP BY grouping_element [, ...] ]
    [ HAVING condition [, ...] ]
    [ WINDOW window_name AS ( window_definition ) [, ...] ]
    [ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] select ]
    [ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ]
    [ LIMIT { count | ALL } ]
    [ OFFSET start [ ROW | ROWS ] ]
    [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ]
    [ FOR { UPDATE | NO KEY UPDATE | SHARE | KEY SHARE } [ OF table_name [, ...] ] [ NOWAIT | SKIP LOCKED ] [...] ]

from_item 可以是以下选项之一：

    [ ONLY ] table_name [ * ] [ [ AS ] alias [ ( column_alias [, ...] ) ] ]

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