mysql当前选择的数据库

当前选择的数据库
命令：mysql> select database();

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。