小俊的MySQL笔记day4

Posted 2021-04-01 西京数据分析与商业智能

小俊的MySQL笔记day4

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 Namefrom employee_datawhere 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。

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