PostgreSQL 9.6.0 文档
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CONNECT

Name

CONNECT -- 建立一个数据库连接

Synopsis

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

描述

CONNECT命令在客户端和 PostgreSQL 服务器之间建立一个连接。

参数

connection_target

connection_target以下列形式之一指定连接的目标服务器。

[ database_name ] [ @host ] [ :port ]

通过 TCP/IP 连接

unix:postgresql://host [ :port ] / [ database_name ] [ ?connection_option ]

通过 Unix 域套接字

tcp:postgresql://host [ :port ] / [ database_name ] [ ?connection_option ]

通过 TCP/IP 连接

SQL string constant

包含上述形式之一的一个值

host variable

类型char[]或VARCHAR[]的主变量，它包含上述形式之一的一个值

connection_object

用于该连接的一个可选标识符，这样可以在其他命令中引用它。这可以是一个 SQL 标识符或者一个主变量。

connection_user

用于数据库连接的用户名。

使用 user_name/password、 user_name IDENTIFIED BY password或者 user_name USING password之一，这个参数也能指定用户名和口令.

用户名和口令可以是 SQL 标识符、字符串常量或者主变量。

DEFAULT

按 libpq 的定义使用所有默认连接参数。

例子

这里是一些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;

这里是一个展示使用主变量指定连接参数的例子程序： 

int
main(void)
{
EXEC SQL BEGIN DECLARE SECTION;
    char *dbname     = "testdb";    /* 数据库名 */
    char *user       = "testuser";  /* 连接用户名 */
    char *connection = "tcp:postgresql://localhost:5432/testdb";
                                    /* 连接字符串 */
    char ver[256];                  /* 存储版本字符串的缓冲区 */
EXEC SQL END DECLARE SECTION;

    ECPGdebug(1, stderr);

    EXEC SQL CONNECT TO :dbname USER :user;
    EXEC SQL SELECT version() INTO :ver;
    EXEC SQL DISCONNECT;

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

    EXEC SQL CONNECT TO :connection USER :user;
    EXEC SQL SELECT version() INTO :ver;
    EXEC SQL DISCONNECT;

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

    return 0;
}

兼容性

SQL 标准中说明了CONNECT，但是连接参数的格式是与实现相关的。

参见

DISCONNECT, SET CONNECTION
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