贤者时间太久了么？--MySQL继续玩_MySQL

1、MySQL

-----运算符和函数-----

字符函数，数值运算符，比较运算等

----字符函数

---

CONCAT()--字符连接

CONCAT_WS()--使用指定的分隔符进行字符连接

mysql> SELECT CONCAT('imooc','-','MySQL');

+-----------------------------+

| CONCAT('imooc','-','MySQL') |

+-----------------------------+

| imooc-MySQL |

+-----------------------------+

mysql> USE TEST;

Database changed

mysql> SELECT * FROM TEST;

+----+----------+

| id | username |

+----+----------+

| 1 | Tom |

| 2 | Ben |

+----+----------+

2 rows in set (0.02 sec)

mysql> SELECT CONCAT(id,username) AS fullname FROM test;

+----------+

| fullname |

+----------+

| 1Tom |

| 2Ben |

+----------+

以上是CONCAT()的实例，而CONCAT_WS()如下

mysql> SELECT CONCAT_WS('-',id,username) FROM test;

+----------------------------+

| CONCAT_WS('-',id,username) |

+----------------------------+

| 1-Tom |

| 2-Ben |

+----------------------------+

CONCAT_WS()需要至少三个参数，第一个是分隔符，后面才是需要连接的东西

---

FORMAT()，数字格式化

mysql> SELECT FORMAT(234234.23423,2);

+------------------------+

| FORMAT(234234.23423,2) |

+------------------------+

| 234,234.23 |

+------------------------+

就是标准化，当然是外国人那一套

---

LOWER()&UPPER()，大小写变换

---

LEFT()&RIGHT()，获取左右侧字符

需要两位参数,从哪个字段取，从第几位开始的左右侧

mysql> SELECT UPPER(LEFT('andy',1));

+-----------------------+

| UPPER(LEFT('andy',1)) |

+-----------------------+

| A |

+-----------------------+

---

LENGTH()，获取字符串长度。注意，空格也要算在内

---

LTRIM(),RTRIM(),TRIM()，删除前/后/前后的空格

TRIM还能删除其他字符

mysql> SELECT TRIM(LEADING '!' FROM '!!!ANDY!!');

+------------------------------------+

| TRIM(LEADING '!' FROM '!!!ANDY!!') |

+------------------------------------+

| ANDY!! |

+------------------------------------+

1 row in set (0.00 sec)

mysql> SELECT TRIM(BOTH '!' FROM '!!!ANDY!!');

+---------------------------------+

| TRIM(BOTH '!' FROM '!!!ANDY!!') |

+---------------------------------+

| ANDY |

+---------------------------------+

1 row in set (0.00 sec)

mysql> SELECT TRIM(TRAILING '!' FROM '!!!ANDY!!');

+-------------------------------------+

| TRIM(TRAILING '!' FROM '!!!ANDY!!') |

+-------------------------------------+

| !!!ANDY |

+-------------------------------------+

1 row in set (0.00 sec)

---

REPLACE()

mysql> SELECT REPLACE('!!ANDY!SDL!!','!','');

+--------------------------------+

| REPLACE('!!ANDY!SDL!!','!','') |

+--------------------------------+

| ANDYSDL |

+--------------------------------+

1 row in set (0.00 sec)

mysql> SELECT REPLACE('!!ANDY!SDL!!','!','LALAL');

+-------------------------------------+

| REPLACE('!!ANDY!SDL!!','!','LALAL') |

+-------------------------------------+

| LALALLALALANDYLALALSDLLALALLALAL |

+-------------------------------------+

1 row in set (0.00 sec)

可以看到，替换是比较灵活的

---

SUBSTRING()

mysql> SELECT SUBSTRING('MYSQL','1','2');

+----------------------------+

| SUBSTRING('MYSQL','1','2') |

+----------------------------+

| MY |

+----------------------------+

1 row in set (0.00 sec)

注意mysql是从1开始，不是从0开始数数

---

做匹配

mysql> SELECT 'mysql' LIKE 'M%';

+-------------------+

| 'mysql' LIKE 'M%' |

+-------------------+

| 1 |

+-------------------+

1 row in set (0.00 sec)

mysql> SELECT * FROM test WHERE username LIKE '%m%';

+----+----------+

| id | username |

+----+----------+

| 1 | Tom |

+----+----------+

这里，%代表任意，类似window中的*

_代表任意一个字符

----数值运算符以及函数

几个很通用的函数简单的介绍下

CEIL()-向上取整---------FLOOR()-向下取整

DIV()-整数除法，也就是结果只有整数

MOD()-取余数

POWER()-幂运算

ROUND()-四舍五入

TRUNCATE()-数字截取（不再四舍五入）

不是两位参数，就是一位参数，大家自己试试哈

----比较运算符与函数

---

[NOT] BETWEEN...AND...

mysql> SELECT 123 BETWEEN 2 AND 123123;

+--------------------------+

| 123 BETWEEN 2 AND 123123 |

+--------------------------+

| 1 |

+--------------------------+

---

[NOT] IN()，给定几个区间来做判断

mysql> SELECT 123 IN(123,23,12);

+-------------------+

| 123 IN(123,23,12) |

+-------------------+

| 1 |

+-------------------+

1 row in set (0.00 sec)

mysql> SELECT 123 IN(120,23,12);

+-------------------+

| 123 IN(120,23,12) |

+-------------------+

| 0 |

+-------------------+

---

IS [NOT] NULL,判断是空么

mysql> SELECT 0 IS NULL;

+-----------+

| 0 IS NULL |

+-----------+

| 0 |

+-----------+

常用在检查是否为空

mysql> SELECT * FROM test WHERE username IS NULL;

Empty set (0.00 sec)

----日期时间函数

---

NOW()，返回当时的日期和时间

CURDATE(),CURTIME()

---

DATE_ADD()，当前日期的变化

mysql> SELECT DATE_ADD('2012-2-23', INTERVAL 234 DAY);

+-----------------------------------------+

| DATE_ADD('2012-2-23', INTERVAL 234 DAY) |

+-----------------------------------------+

| 2012-10-14 |

+-----------------------------------------+

1 row in set (0.00 sec)

mysql> SELECT DATE_ADD('2012-2-23', INTERVAL -234 DAY);

+------------------------------------------+

| DATE_ADD('2012-2-23', INTERVAL -234 DAY) |

+------------------------------------------+

| 2011-07-04 |

+------------------------------------------+

1 row in set (0.00 sec)

---

DATEDIFF()，得到两个日期间的差值

mysql> SELECT DATEDIFF('2304-2-2','1234-3-22');

+----------------------------------+

| DATEDIFF('2304-2-2','1234-3-22') |

+----------------------------------+

| 390760 |

+----------------------------------+

1 row in set (0.02 sec)

---

DATE_FORMAT()，日期的格式化，日期的格式是可以选的，也就是说日期的格式转换

mysql> SELECT DATE_FORMAT('2013-2-22','%m/%d/%y');

+-------------------------------------+

| DATE_FORMAT('2013-2-22','%m/%d/%y') |

+-------------------------------------+

| 02/22/13 |

+-------------------------------------+

1 row in set (0.00 sec)

----信息函数

USER(),VERSION(),DATEBASE(),CONNECTION_ID(),LAST_INSERT_ID()

----聚合函数

只有一个返回值是他们的特点

AVG(),COUNT(),MAX(),MIN(),SUM()

直接调用可能会有错误，一般是针对数据表的字段进行的操作

mysql> SELECT AVG(id) FROM test;

+---------+

| AVG(id) |

+---------+

| 1.5000 |

+---------+

----加密函数

MD5(),PASSWORD()

mysql> SELECT MD5('HELLOWORLD');

+----------------------------------+

| MD5('HELLOWORLD') |

+----------------------------------+

| e81e26d88d62aba9ab55b632f25f117d |

+----------------------------------+

1 row in set (0.00 sec)

mysql> SELECT PASSWORD('HELLOWORLD');

+-------------------------------------------+

| PASSWORD('HELLOWORLD') |

+-------------------------------------------+

| *3456E7782A7F539BC823C715DB60231B0C7DE847 |

+-------------------------------------------+

1 row in set (0.00 sec)

一般而言，网页的编程用的都是MD5，password仅仅用于修改当前用户的密码

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注重自带函数的熟悉、了解，灵活的调用和嵌套运用