MySQL day5---运算符和函数

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------Chapter6------------------------------------------------

1.字符函数

CONCAT() 字符连接

eg:

mysql> SELECT CONCAT('imooc','mysql');
+-------------------------+
| CONCAT('imooc','mysql') |
+-------------------------+
| imoocmysql |

SELECT CONCAT(firstname,lastname) AS fullname FROM test1;
+----------+
| fullname |
+----------+
| AB       |
| CD       |
| tom%123 |
| NULL     |
+----------+
4 rows in set (0.00 sec)

CONCAT_WS() 使用指定的分隔符进行字符连接

eg:

SELECT CONCAT_WS('|','A','B','C');
+----------------------------+
| CONCAT_WS('|','A','B','C') |
+----------------------------+
| A|B|C |
+----------------------------+
1 row in set (0.00 sec)

FORMAT() 数字格式化

eg:

SELECT FORMAT(12560.75,1);
+--------------------+
| FORMAT(12560.75,1) |
+--------------------+
| 12,560.8 |
+--------------------+
1 row in set (0.02 sec)

LOWER() 转换成小写字母

eg:

SELECT LOWER('MySQL');
+----------------+
| LOWER('MySQL') |
+----------------+
| mysql |
+----------------+
1 row in set (0.00 sec)

UPPER() 转换成大写字母

LEFT() 获取左侧字符

eg:

SELECT LEFT('MYSQL',2); MY

RIGHT() 获取右侧字符

LENGTH() 获取字符串长度

eg:SELECT LENGTH(' MYSQL    ');
+-----------------------+
| LENGTH(' MYSQL    ') |
+-----------------------+
|                    11 |
+-----------------------+
1 row in set (0.00 sec)

LTRIM() 删除前导空格

eg:SELECT LENGTH(LTRIM(' MYSQL ')); 9

SELECT LENGTH(RTRIM(' MYSQL ')); 7

SELECT LENGTH(TRIM(' MYSQL ')); 5

RTRIM() 删除后导空格

eg:

SELECT TRIM(LEADING '?' FROM '??MYSQL???');
+-------------------------------------+
| MYSQL??? |
+-------------------------------------+

mysql> SELECT TRIM(TRAILING '?' FROM '??MYSQL???');

+--------------------------------------+
| ??MYSQL |
+--------------------------------------+

mysql> SELECT TRIM(BOTH '?' FROM '??MYSQL???');
+----------------------------------+
| MYSQL |
+----------------------------------+

SUBSTRING() 删除前导和后续空格

SELECT SUBSTRING('MYSQL',1,2);
+------------------------+
| MY |
+------------------------+

[NOT] LIKE 模式匹配

REPLACE() 字符串替换

eg: SELECT REPLACE('??My??SQL???','?','');
+--------------------------------+
| MySQL |
+--------------------------------+

2.数值运算符和函数

CEIL() 进一取整

DIV 整数除法

FLOOR() 舍一取整

MOD 取余数

POWER() 幂运算

ROUND() 四舍五入

TRUNCATE() 数字截取

3.比较运算符和函数

[NOT] BETWEEN ... AND ... [不]在范围之内

[NOT] IN() [不]在列出值范围内

[NOT] NULL() [不]为空

4.日期时间函数

NOW() 当前日期和时间

CURDATE() 当前日期

CURTIME() 当前时间

DATE_ADD() 日期变化

eg:

SELECT DATE_ADD('2015-3-12',INTERVAL - 365 DAY);
+------------------------------------------+
| DATE_ADD('2015-3-12',INTERVAL - 365 DAY) |
+------------------------------------------+
| 2014-03-12 |
+------------------------------------------+

DATEDIFF() 日期差值

eg:

SELECT DATEDIFF('2011-3-12','2012-3-12');
+-----------------------------------+
| DATEDIFF('2011-3-12','2012-3-12') |
+-----------------------------------+
| -366 |
+-----------------------------------+
1 row in set (0.00 sec)

DATE_FORMAT() 日期格式化

eg:

SELECT DATE_FORMAT('2014-3-12','%m/%d/%Y');
+-------------------------------------+
| DATE_FORMAT('2014-3-12','%m/%d/%Y') |
+-------------------------------------+
| 03/12/2014 |
+-------------------------------------+
1 row in set (0.00 sec)

5.信息函数

CONNECTION_ID() 连接ID

DATEBASE() 当前数据库

LAST_INSERT_ID() 最后插入记录的ID号

USER() 当前用户

VERSION() 版本信息

6.聚合函数

AVG() 平均值

COUNT() 计数

MAX() 最大值

MIN() 最小值

SUM() 求和

7.加密函数

MD5() 信息摘要算法

eg:

SELECT MD5('ADMIN');
+----------------------------------+
| MD5('ADMIN') |
+----------------------------------+
| 73acd9a5972130b75066c82595a1fae3 |
+----------------------------------+

PASSWORD() 密码算法

eg：SET PASSWORD = PASSWORD('root');

SELECT PASSWORD('ADMIN');

+-------------------------------------------+
| PASSWORD('ADMIN') |
+-------------------------------------------+
| *0B0A27832C339662F96E0238AD92FCBCB992A7EA |
+-------------------------------------------+

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