CONNECT — 建立一个数据库连接
CONNECT TOconnection_target[ ASconnection_name] [ USERconnection_user] CONNECT TO DEFAULT CONNECTconnection_userDATABASEconnection_target
CONNECT命令在客户端和 PostgreSQL 服务器之间建立一个连接。
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
包含上述形式之一的一个值
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/passworduser_name IDENTIFIED BY passworduser_name USING password
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。
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;
}
SQL 标准中说明了CONNECT，但是连接参数的格式是与实现相关的。