大约 2 分钟
CONNECT
CONNECT — 建立一个数据库连接
大纲
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 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
SQL 标准中说明了CONNECT，但是连接参数的格式是与实现相关的。