# 连接

CONNECT — 建立数据库连接

# 概要

CONNECT TO connection_target [ AS connection_name ] [ USER connection_user ]
CONNECT TO DEFAULT
CONNECT connection_user
DATABASE connection_target

# 描述

连接命令在客户端和 PostgreSQL 服务器之间建立连接。

# 参数

连接目标

*连接目标*以多种形式之一指定连接的目标服务器。

[ 数据库名称 ][ @host ] [ :**港口 ]

通过 TCP/IP 连接

unix:postgresql://主持人 [ :港口 ] / [ 数据库名称 ][ ?connection_option ]

通过 Unix 域套接字连接

tcp:postgresql://主持人 [ :港口 ] / [ 数据库名称 ][ ?connection_option ]

通过 TCP/IP 连接

SQL 字符串常量

包含上述形式之一的值

主变量

类型的主变量字符[]或者VARCHAR[]包含上述形式之一的值

连接名称

连接的可选标识符,以便可以在其他命令中引用。这可以是 SQL 标识符或主机变量。

连接用户

数据库连接的用户名。

该参数还可以指定用户名和密码,使用形式之一*用户名*/*密码*,*用户名* 由 * 识别密码*, 要么*用户名* 使用 *密码*.

用户名和密码可以是 SQL 标识符、字符串常量或主机变量。

默认

使用 libpq 定义的所有默认连接参数。

# 例子

这里有几个用于指定连接参数的变体:

EXEC SQL CONNECT TO "connectdb" AS main;
EXEC SQL CONNECT TO "connectdb" AS second;
EXEC SQL CONNECT TO "unix:postgresql://200.46.204.71/connectdb" AS main USER connectuser;
EXEC SQL CONNECT TO "unix:postgresql://localhost/connectdb" AS main USER connectuser;
EXEC SQL CONNECT TO 'connectdb' AS main;
EXEC SQL CONNECT TO 'unix:postgresql://localhost/connectdb' AS main USER :user;
EXEC SQL CONNECT TO :db AS :id;
EXEC SQL CONNECT TO :db USER connectuser USING :pw;
EXEC SQL CONNECT TO @localhost AS main USER connectdb;
EXEC SQL CONNECT TO REGRESSDB1 as main;
EXEC SQL CONNECT TO AS main USER connectdb;
EXEC SQL CONNECT TO connectdb AS :id;
EXEC SQL CONNECT TO connectdb AS main USER connectuser/connectdb;
EXEC SQL CONNECT TO connectdb AS main;
EXEC SQL CONNECT TO connectdb@localhost AS main;
EXEC SQL CONNECT TO tcp:postgresql://localhost/ USER connectdb;
EXEC SQL CONNECT TO tcp:postgresql://localhost/connectdb USER connectuser IDENTIFIED BY connectpw;
EXEC SQL CONNECT TO tcp:postgresql://localhost:20/connectdb USER connectuser IDENTIFIED BY connectpw;
EXEC SQL CONNECT TO unix:postgresql://localhost/ AS main USER connectdb;
EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb AS main USER connectuser;
EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb USER connectuser IDENTIFIED BY "connectpw";
EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb USER connectuser USING "connectpw";
EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb?connect_timeout=14 USER connectuser;

下面是一个示例程序,它说明了使用主机变量来指定连接参数:

int
main(void)
{
EXEC SQL BEGIN DECLARE SECTION;
    char *dbname     = "testdb";    /* database name */
    char *user       = "testuser";  /* connection user name */
    char *connection = "tcp:postgresql://localhost:5432/testdb";
                                    /* connection string */
    char ver[256];                  /* buffer to store the version string */
EXEC SQL END DECLARE SECTION;

    ECPGdebug(1, stderr);

    EXEC SQL CONNECT TO :dbname USER :user;
    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;
    EXEC SQL SELECT version() INTO :ver;
    EXEC SQL DISCONNECT;

    printf("version: %s\n", ver);

    EXEC SQL CONNECT TO :connection USER :user;
    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;
    EXEC SQL SELECT version() INTO :ver;
    EXEC SQL DISCONNECT;

    printf("version: %s\n", ver);

    return 0;
}

# 兼容性

连接在 SQL 标准中指定,但连接参数的格式是特定于实现的。

# 也可以看看

断开, 设置连接