排序：order by

/*语法格式：
    select 
        ename,sal
    from
        emp
    order by
        sal; // 默认是升序！！
 */
//指定降序： desc
//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 |
            +--------+---------+
//指定升序： asc
//mysql> select ename,sal from emp order by sal asc ;
            +--------+---------+
            | 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 |
            +--------+---------+
以两个字段排序吗？或者说按照多个字段排序？
查询员工名字和薪资，要求按照薪资升序，如果薪资一样的话，再按照名字升序排列。
    select 
        ename,sal
    from
        emp
    order by
        sal asc, ename asc; // sal在前，起主导，只有sal相等的时候，才会考虑启用ename排序。
了解：根据字段位置也可以排序
mysql> select ename,sal from emp order by 2;//2表示第二列，第二列是sal
//按照查询结果的第二列sal排序
            +--------+---------+
            | 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 |
            +--------+---------+
只了解一下，不建议在开发中这样使用，不健壮
因为列的顺序很容易发生改变，列顺序修改后，2就废了

//找出薪资在1250到3000之间的员工信息，要求按照薪资降序排列
select 
      ename,sal
 from 
       emp
 where 
       sal between 1250 and 3000
 order by
       sal desc;
 mysql> select ename,sal from emp where sal between 1250 and 3000 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 |
        +--------+---------+

  关键字顺序不能变
  select
          ……
   from
          ……
   where 
          ……

   order by
          ……;

   以上语句的执行顺序必须掌握：
     第一步： from(先到表中)
     第二步： where(筛选)
     第三步： select(查找出来)
     第四步： order by (排序总是在最后执行)