CONNECT

CONNECT
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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 命令在客户端与 PostgreSQL 服务器之间建立一条连接。

参数

connection_target #

connection_target 以若干种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 域套接字连接
tcp:postgresql://host [ :port ] / [ database_name ] [ ?connection_option ] #: 通过 TCP/IP 连接
SQL string constant #: 包含上述形式之一取值
host variable #: 类型为 char[] 或 VARCHAR[] 的主变量，包含上述形式之一取值

connection_name #

连接的一个可选标识符，以便在其他命令中引用该连接。它可以是一个 SQL 标识符或一个主变量。

connection_user #

该数据库连接的用户名。

这个参数也可以用 user_name/password、 user_name IDENTIFIED BY password 或 user_name USING password 之一的形式同时指定用户名和密码。

用户名和密码可以是 SQL 标识符、字符串常量或主变量。

DEFAULT #

使用 libpq 定义的所有默认连接参数。

示例

下面是指定连接参数的几种变体：

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，说明如何使用主变量指定连接参数：

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

CONNECT 在 SQL 标准中有规定，但连接参数的格式由具体实现决定。

另请参阅

DISCONNECT, SET CONNECTION

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