mysql查询常用指令

mysql查询
（1）查询数据表的所有记录

select * from students;

（2）查询特定字段的信息

select ke_name,ke_tea_num from cources;
+----------+------------+
| ke_name  | ke_tea_num |
+----------+------------+
| ke_one   |       3014 |
| ke_two   |       3011 |
| ke_three |       3013 |
| ke_four  |       3012 |
+----------+------------+

（3）查询并排重——distinct关键字

select distinct num from score;

（4）查询区间——where +between +and 或者 where > 80 and < （直接使用运算符比较）

 select * from score where score between 80 and 90;

select * from score where score> 80 and score < 90;

(5)查询 或 关系，什么或什么或什么——in( , , )

select * from score where score in(85,86,87);

（6）不同字段的 或 关系——or 关键字

select * from score where ke_num=2 or score >80;

（7） 不同字段的且 关系——and关键字

mysql> select * from score where ke_num=2 and score >80;

（8）升序降序查询——order by asc为升序，order by desc为降序

 select * from score where ke_num=2 order by score desc;

设定两列一列升序、一列降序——固定格式：order by A asc，B desc;(逗号不能换成and)

select * from score order by ke_num asc,score desc;
+------+--------+-------+
| num  | ke_num | score |
+------+--------+-------+
| 2001 |      1 |    93 |
| 2005 |      1 |    87 |
| 2007 |      1 |    58 |
| 2004 |      2 |    91 |
| 2009 |      2 |    84 |
| 2002 |      2 |    83 |
| 2005 |      2 |    71 |
| 2007 |      3 |    97 |
| 2001 |      3 |    84 |
| 2006 |      3 |    78 |
| 2003 |      3 |    74 |
| 2008 |      4 |    95 |
| 2003 |      4 |    94 |
| 2009 |      4 |    91 |
+------+--------+-------+

（9）统计查询

mysql> select count(*) from score where score between 80 and 90;

（10）max min查询——max（）或min()或者排序查询

select max(score) from score ;
+------------+
| max(score) |
+------------+
|         97 |
+------------+

当最值出现重复时，

select * from students where stu_num=(select num from score where score=(select max(score) from score));
ERROR 1242 (21000): Subquery returns more than 1 row

使用非排序的方法可以分两步：

 select num from score where score=(select max(score) from score);
  select * from students where stu_num in(2004,2007);

合起来用一个in关键字就能实现

select * from students where stu_num in (select num from score where score=(select max(score) from score));

使用排序的方法：

select num from score order by score desc limit 0,5;

但是limit和in不能一起使用。只能分两步。

select * from students where stu_num in(select num from score order by score desc limit 0,5);
ERROR 1235 (42000): This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'

（11）子查询

select num from score where score=(select max(score) from score);
+------+
| num  |
+------+
| 2007 |
+------+

 select * from students where stu_num=(select num from score where score=(select max(score) from score));
+---------+----------+
| stu_num | stu_name |
+---------+----------+
|    2007 | xiaoqi   |
+---------+----------+

（12）查询平均、分组平均

select avg(score)from score where ke_num=2;
+------------+
| avg(score) |
+------------+
|    83.7500 |
+------------+

分组平均——group by关键字

select avg(score) from score group by ke_num;

select ke_num, avg(score) from score group by ke_num;
+--------+------------+
| ke_num | avg(score) |
+--------+------------+
|      1 |    79.3333 |
|      2 |    83.7500 |
|      3 |    83.2500 |
|      4 |    93.3333 |
+--------+------------+

至少有几条记录——having count(*)关键字

select ke_num,avg(score)from score group by ke_num having count(*)>=4;//至少有几条记录

（13）like关键字用于匹配

 select tea_name from teachers where tea_name like 'shi%';
+----------+
| tea_name |
+----------+
| shiyi    |
| shier    |
| shisan   |
| shisi    |
| shiwu    |
+----------+

（14）查询不同的表中的字段对某一字段的限制——多表查询
//从students中选出，score表中成绩大于90的同学。

select stu_name,ke_num,score from students,score
    -> where students.stu_num=score.num and score.score>90;

（15）查询所有学生的姓名、课程名称、成绩、任课教师姓名

 select stu_name,ke_name,score,tea_name from students,cources,score,teachers
    -> where score.num=students.stu_num and score.ke_num=cources.ke_num and cources.ke_tea_num=teachers.tea_num;

查表先分开查询，然后按照两表的共有字段进行匹配，最终把表合并。
（16）查询选修1课程并且比2007号同学1课程成绩高的同学。

select * from score where ke_num=1 and score>(select score from score where num=2007 and ke_num=1);
+------+--------+-------+
| num  | ke_num | score |
+------+--------+-------+
| 2001 |      1 |    93 |
| 2005 |      1 |    87 |
+------+--------+-------+

（17）查询与年份有关的

select year(birthday) from students where sno in(108,101);

(18)查询某任课老师所教授课程的名称

select ke_name from cources where ke_tea_num=(select tea_num from teachers where tea_name='shiyi');

（19）查询选修某门课的学生数大于3的教师的名单

select tea_name from teachers where tea_num in(select ke_tea_num from cources where ke_num in(select ke_num from score group by ke_num having count(*)>3));
+----------+
| tea_name |
+----------+
| shiyi    |
| shisan   |
+----------+

（20）查看女老师教授的课程的得分情况

 select * from score where ke_num in(select ke_num from cources where ke_tea_num in (select tea_num from teachers where tea_sex='F' ));