CONNECT · PostgreSQL 中文文檔 9.3

# CONNECT ## Name CONNECT?--?建立數據庫連接 ## Synopsis ``` CONNECT TO _connection_target_ [ AS _connection_name_ ] [ USER _connection_user_name_ ] CONNECT TO DEFAULT CONNECT _connection_user_name_ DATABASE _connection_target_ ``` ## 描述 `CONNECT`命令在客戶端和PostgreSQL服務器之間創建了連接。 ## 參數 `_connection_target_` `_connection_target_` 在幾種形式之一上指定了連接的目標服務器。 [ `_database_name_` ] [ `@``_host_` ] [ `:``_port_` ] TCP/IP連接 `unix:postgresql://``_host_` [ `:``_port_` ] `/` [ `_database_name_` ] [ `?``_connection_option_` ] 連接Unix-域套接字 `tcp:postgresql://``_host_` [ `:``_port_` ] `/` [ `_database_name_` ] [ `?``_connection_option_` ] TCP/IP連接 SQL字符串常量在上述形式之一中包含一個值宿主變量類型`char[]` 或者`VARCHAR[]`的宿主變量包含上述形式之一的值。 `_connection_object_` 用于連接可選標識符，這樣就可以指向其他命令。這可以是一個SQL標識符或者宿主變量。 `_connection_user_` 用于數據庫連接的用戶名。該參數可以指定用戶名和密碼，使用下面形式之一 `_user_name_`/`_password_`, `_user_name_` IDENTIFIED BY `_password_`或者 `_user_name_` USING `_password_`. 用戶名和密碼可以是SQL標識符，字符串常量，或者宿主變量。 `DEFAULT` 使用所有缺省連接參數，正如通過libpq定義的。 ## 例子指定連接參數的幾種變形： ``` 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; ``` 這里有一個例子程序闡述了使用宿主變量指定連接參數： ``` int main(void) { EXEC SQL BEGIN DECLARE SECTION; char *dbname = "testdb"; /*數據庫名稱*/ char *user = "testuser"; /*連接用戶名*/ char *connection = "tcp:postgresql://localhost:5432/testdb"; /* 連接字符串 */ char ver[256]; /*存儲版本字符串的緩沖區*/ 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; } ``` ## 兼容性在SQL標準中聲明`CONNECT`，但是連接參數的格式是具體實施的。 ## 參見 [DISCONNECT](#calibre_link-27), [SET CONNECTION](#calibre_link-2019)