MySQL 启动、关闭、选择数据库等命令

MySQL中SELECT命令类似于其他编程语言里的print或者write，你可以用它来显示一个字符串、数字、数学表达式的结果等等。如何使用MySQL中SELECT命令的特殊功能？

1.显示MYSQL的版本mysql> select version(); +-----------------------+ | version()             | +-----------------------+ | 6.0.4-alpha-community | +-----------------------+ 1 row in set (0.02 sec) 

2. 显示当前时间mysql> select now(); +---------------------+ | now()               | +---------------------+ | 2009-09-15 22:35:32 | +---------------------+ 1 row in set (0.04 sec) 

3. 显示年月日SELECT DAYOFMONTH(CURRENT_DATE); +--------------------------+ | DAYOFMONTH(CURRENT_DATE) | +--------------------------+ |                       15 | +--------------------------+ 1 row in set (0.01 sec)   SELECT MONTH(CURRENT_DATE); +---------------------+ | MONTH(CURRENT_DATE) | +---------------------+ |                   9 | +---------------------+ 1 row in set (0.00 sec)   SELECT YEAR(CURRENT_DATE); +--------------------+ | YEAR(CURRENT_DATE) | +--------------------+ |               2009 | +--------------------+ 1 row in set (0.00 sec) 

4. 显示字符串mysql> SELECT "welecome to my blog!"; +----------------------+ | welecome to my blog! | +----------------------+ | welecome to my blog! | +----------------------+ 1 row in set (0.00 sec) 

5. 当计算器用select ((4 * 4) / 10 ) + 25; +----------------------+ | ((4 * 4) / 10 ) + 25 | +----------------------+ |                26.60 | +----------------------+ 1 row in set (0.00 sec) 

6. 串接字符串select CONCAT(f_name, " ", l_name) AS Name from employee_data where title = 'Marketing Executive'; +---------------+ | Name          | +---------------+ | Monica Sehgal | | Hal Simlai    | | Joseph Irvine | +---------------+ 3 rows in set (0.00 sec) 注意：这里用到CONCAT()函数，用来把字符串串接起来。另外，我们还用到以前学到的AS给结果列'CONCAT(f_name, " ", l_name)'起了个假名。