1.排序
2.单行处理函数
内容转小写
内容转大写
取子串
字符串拼接
求长度
去除前后空白
四舍五入
生成随机数
空转换
1.排序示例表内容见此篇文章
Mysql支持数据排序操作，例如，现在我们按照工资从小到大进行排序操作：
mysql> select ename,sal from emp order by sal;
+--------+---------+
| ename | sal |
+--------+---------+
| SMITH | 800.00 |
| JAMES | 950.00 |
| ADAMS | 1100.00 |
| WARD | 1250.00 |
| MARTIN | 1250.00 |
| MILLER | 1300.00 |
| TURNER | 1500.00 |
| ALLEN | 1600.00 |
| CLARK | 2450.00 |
| BLAKE | 2850.00 |
| JONES | 2975.00 |
| SCOTT | 3000.00 |
| FORD | 3000.00 |
| KING | 5000.00 |
+--------+---------+
14 rows in set (0.00 sec)
如果需要降序排序的话，需要指定desc：（默认为升序排序，如果您进行指定的话，指定为asc即可）
mysql> select ename,sal from emp order by sal desc;
+--------+---------+
| ename | sal |
+--------+---------+
| KING | 5000.00 |
| SCOTT | 3000.00 |
| FORD | 3000.00 |
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| ALLEN | 1600.00 |
| TURNER | 1500.00 |
| MILLER | 1300.00 |
| WARD | 1250.00 |
| MARTIN | 1250.00 |
| ADAMS | 1100.00 |
| JAMES | 950.00 |
| SMITH | 800.00 |
+--------+---------+
14 rows in set (0.00 sec)
更复杂的情况，为多字段排序：
比如我们想按照薪资升序排列，薪资一样的情况下，按照名字降序排序：
mysql> select ename,sal from emp order by sal,ename desc;
+--------+---------+
| ename | sal |
+--------+---------+
| SMITH | 800.00 |
| JAMES | 950.00 |
| ADAMS | 1100.00 |
| WARD | 1250.00 |
| MARTIN | 1250.00 |
| MILLER | 1300.00 |
| TURNER | 1500.00 |
| ALLEN | 1600.00 |
| CLARK | 2450.00 |
| BLAKE | 2850.00 |
| JONES | 2975.00 |
| SCOTT | 3000.00 |
| FORD | 3000.00 |
| KING | 5000.00 |
+--------+---------+
14 rows in set (0.00 sec)
排序结合条件进行查找：
要求找出薪资在1250到3500之间，按照薪资降序排序：
mysql> select ename,sal from emp where sal between 1250 and 3500 order by sal desc;
+--------+---------+
| ename | sal |
+--------+---------+
| SCOTT | 3000.00 |
| FORD | 3000.00 |
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| ALLEN | 1600.00 |
| TURNER | 1500.00 |
| MILLER | 1300.00 |
| WARD | 1250.00 |
| MARTIN | 1250.00 |
+--------+---------+
10 rows in set (0.00 sec)
2.单行处理函数
处理完一行再处理下一行：（一个输入对应一个输出）
内容转小写mysql> select lower(ename) from emp;
+--------------+
| lower(ename) |
+--------------+
| smith |
| allen |
| ward |
| jones |
| martin |
| blake |
| clark |
| scott |
| king |
| turner |
| adams |
| james |
| ford |
| miller |
+--------------+
14 rows in set (0.00 sec)
内容转大写
mysql> select upper(ename) from emp;
+--------------+
| upper(ename) |
+--------------+
| SMITH |
| ALLEN |
| WARD |
| JONES |
| MARTIN |
| BLAKE |
| CLARK |
| SCOTT |
| KING |
| TURNER |
| ADAMS |
| JAMES |
| FORD |
| MILLER |
+--------------+
14 rows in set (0.00 sec)
取子串
例如：我们想要取到每个名字的第一个字母：
mysql> select substr(ename,1,1) from emp;
+-------------------+
| substr(ename,1,1) |
+-------------------+
| S |
| A |
| W |
| J |
| M |
| B |
| C |
| S |
| K |
| T |
| A |
| J |
| F |
| M |
+-------------------+
14 rows in set (0.00 sec)
字符串拼接
拼接每个人的empno和ename：
mysql> select concat(empno,ename) from emp;
+---------------------+
| concat(empno,ename) |
+---------------------+
| 7369SMITH |
| 7499ALLEN |
| 7521WARD |
| 7566JONES |
| 7654MARTIN |
| 7698BLAKE |
| 7782CLARK |
| 7788SCOTT |
| 7839KING |
| 7844TURNER |
| 7876ADAMS |
| 7900JAMES |
| 7902FORD |
| 7934MILLER |
+---------------------+
14 rows in set (0.00 sec)
求长度
取出每个人名字的字符数：
mysql> select length(ename) from emp;
+---------------+
| length(ename) |
+---------------+
| 5 |
| 5 |
| 4 |
| 5 |
| 6 |
| 5 |
| 5 |
| 5 |
| 4 |
| 6 |
| 5 |
| 5 |
| 4 |
| 6 |
+---------------+
14 rows in set (0.00 sec)
去除前后空白
查询名字为KING的详细信息，不包含前后空白：
mysql> select * from emp where ename = trim('KING ');
+-------+-------+-----------+------+------------+---------+------+--------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
+-------+-------+-----------+------+------------+---------+------+--------+
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 |
+-------+-------+-----------+------+------------+---------+------+--------+
1 row in set (0.00 sec)
四舍五入
对123.456保留0位小数
mysql> select round(123.456,0) from emp;
+------------------+
| round(123.456,0) |
+------------------+
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
| 123 |
+------------------+
14 rows in set (0.00 sec)
生成随机数
生成0到1的随机小数：
mysql> select rand() from emp;
+---------------------+
| rand() |
+---------------------+
| 0.06316715857309024 |
| 0.5963954959031152 |
| 0.7924760345299505 |
| 0.17319371567405176 |
| 0.48854050551405226 |
| 0.923121411281751 |
| 0.1499855706002429 |
| 0.9805636498896066 |
| 0.4528615683809496 |
| 0.3226169229695731 |
| 0.25449994043866164 |
| 0.304648964018234 |
| 0.75974502950883 |
| 0.8847782862230933 |
+---------------------+
14 rows in set (0.00 sec)
空转换
数据库中对于NULL进行运算结果一定为NULL 于是就有了NULL处理函数
例如：计算每个员工的年收入（月薪+月奖金）：
mysql> select ename,job,sal,
-> (case job when 'MANAGER' then sal*1.1 when 'SALESMAN' then sal*1.5 else sal*1.2 end) as newsal
-> from emp;
+--------+-----------+---------+---------+
| ename | job | sal | newsal |
+--------+-----------+---------+---------+
| SMITH | CLERK | 800.00 | 960.00 |
| ALLEN | SALESMAN | 1600.00 | 2400.00 |
| WARD | SALESMAN | 1250.00 | 1875.00 |
| JONES | MANAGER | 2975.00 | 3272.50 |
| MARTIN | SALESMAN | 1250.00 | 1875.00 |
| BLAKE | MANAGER | 2850.00 | 3135.00 |
| CLARK | MANAGER | 2450.00 | 2695.00 |
| SCOTT | ANALYST | 3000.00 | 3600.00 |
| KING | PRESIDENT | 5000.00 | 6000.00 |
| TURNER | SALESMAN | 1500.00 | 2250.00 |
| ADAMS | CLERK | 1100.00 | 1320.00 |
| JAMES | CLERK | 950.00 | 1140.00 |
| FORD | ANALYST | 3000.00 | 3600.00 |
| MILLER | CLERK | 1300.00 | 1560.00 |
+--------+-----------+---------+---------+
14 rows in set (0.00 sec)
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