MySQL筆記之系統信息函數詳解
2024-07-24 12:40:42
供稿：網友
系統信息函數用來查詢mysql數據庫的系統信息 VERSION()返回數據庫版本號 復制代碼 代碼如下: mysql> SELECT VERSION(); +-------------------------+ | VERSION() | +-------------------------+ | 5.5.28-0ubuntu0.12.10.2 | +-------------------------+ row in set (0.00 sec) 我這里用的是基于ubuntu發行版，Linux Mint CONNECTION_ID()返回數據庫的連接次數 復制代碼 代碼如下: mysql> SELECT CONNECTION_ID(); +-----------------+ | CONNECTION_ID() | +-----------------+ | 36 | +-----------------+ row in set (0.00 sec) 其實每次連接到mysql的時候就會有顯示 DATABASE()、SCHEMA()返回當前數據庫名 復制代碼 代碼如下: mysql> SELECT DATABASE(), SCHEMA(); +------------+----------+ | DATABASE() | SCHEMA() | +------------+----------+ | person | person | +------------+----------+ row in set (0.00 sec) USER()、SYSTEM_USER()、SESSION_USER()返回當前用戶 復制代碼 代碼如下: mysql> SELECT USER(), SYSTEM_USER(), SESSION_USER(); +----------------+----------------+----------------+ | USER() | SYSTEM_USER() | SESSION_USER() | +----------------+----------------+----------------+ | root@localhost | root@localhost | root@localhost | +----------------+----------------+----------------+ row in set (0.00 sec) CURRENT_USER()、CURRENT_USER返回當前用戶 復制代碼 代碼如下: mysql> SELECT CURRENT_USER(), CURRENT_USER; +----------------+----------------+ | CURRENT_USER() | CURRENT_USER | +----------------+----------------+ | root@localhost | root@localhost | +----------------+----------------+ row in set (0.00 sec) 上面的三個和這兩個功能是一樣的 CHARSET(str)返回字符串str的字符集 復制代碼 代碼如下: mysql> SELECT CHARSET('張三'); +-------------------+ | CHARSET('張三') | +-------------------+ | utf8 | +-------------------+ row in set (0.00 sec) COLLATION(str)返回字符串str的字符排列方式 復制代碼 代碼如下: mysql> SELECT COLLATION('張三'); +---------------------+ | COLLATION('張三') | +---------------------+ | utf8_general_ci | +---------------------+ row in set (0.00 sec) LAST_INSERT_ID()返回最后生成的AUTO_INCREMENT值 復制代碼 代碼如下: mysql> CREATE TABLE t1(id INT PRIMARY KEY AUTO_INCREMENT); Query OK, 0 rows affected (0.10 sec) mysql> INSERT INTO t1 VALUES(NULL); Query OK, 1 row affected (0.04 sec) mysql> INSERT INTO t1 VALUES(NULL); Query OK, 1 row affected (0.03 sec) mysql> INSERT INTO t1 VALUES(NULL); Query OK, 1 row affected (0.04 sec) mysql> SELECT * FROM t1; +----+ | id | +----+ | 1 | | 2 | | 3 | +----+ rows in set (0.00 sec) mysql> SELECT LAST_INSERT_ID(); +------------------+ | LAST_INSERT_ID() | +------------------+ | 3 | +------------------+ row in set (0.00 sec) 上面的語句首先創建了一張表t1，其中有一個自增字段id 然后分三次插入NULL，使其自增 確認已經存在數據之后，使用LAST_INSERT_ID()獲取最后自動生成的值
