sql语句的实际应用
一、普通多表连接方式：
select * from 表1,表2...WHERE 表1.d_id = 表2.id;
SELECT * FROM 表1，表2... (笛卡尔积)
as别名：
SELECT 属性(姓名年龄之类的) FROM 表1 as one,表2 as two WHERE one.d_id = 表2.id;
内连接：查询两张表的公共部分。
SELECT 列名 FROM 表1 INNER JOIN 表2 ON 表1.列 = 表2.列;
Select * FROM employe as e INNER JOIN deparment as d ON e.d_id AND e.name = '张三';
(左)外连接：左边表会全被查出来，右边关联的会被查出来
SELECT e.name,d.deparment_name FROM employe as e LEFT OUTER JOIN deparment as d ON e.d_id = d.id;SE
(右)外连接：
SELECT e.name,d.deparment_name FROM employe as e RIGHT OUTER JOIN deparment as d ON e.d_id = d.id;
子查询：在查询中还可以有查询
SELECT name as 姓名 FROM student as s WHERE s.d_id = (SELECT id FROM department as d WHERE d.deparment_name = 软件部);
自连接：一张表、必须有id和父id(parent_id)
SELECT s.name as 姓名,f.name as 领导 FROM people as s INNER JOIN people as f ON s.parent_id = f.id AND s.name ='主管';
| id |
name |
Parent_id |
|
id |
name |
| 1 |
总 |
0 |
1 |
总 |
|
| 2 |
经理 |
1 |
2 |
经理 |
|
| 3 |
主管 |
2 |
3 |
主管 |
|
| 4 |
高级 |
3 |
4 |
高级 |
|
| 5 |
初级 |
4 |
5 |
初级 |
自连接为一张表 原表为左表，右表是抽象象出来的。把左表看成子表，右表看成父表
函数： where后面不能加函数
合并：SELECT * FROM student GROUP BY age; (根据年龄相同合并)
合并前：
| name |
age |
number |
| 小明 |
20 |
1001 |
| 小丽 |
20 |
1002 |
| 小刚 |
23 |
1003 |
合并后：
| name |
age |
number |
| 小明 |
20 |
1001 |
| 小刚 |
23 |
1003 |
求和：SELECT SUM(age) as 总年龄 FROM student;
求平均：SELECT AVG(age) as 平均年龄 FROM student;
求平均(保留一位)：SELECT ROUND (AVG(age),1) as 平均年龄 FROM student; (同理保留两位就写2，不保留就是0)
| 总年龄 |
|
平均年龄 |
|
平均年龄 |
| 63 |
|
21.0000000…. |
|
21.0 |
求最大：SELECT MAX(age) as 最大年龄 FROM student;
查询有无记录：SELECT COUNT(id) FROM student;
| 最大年龄 |
|
Count(id) |
| 23 |
|
3 |
二、sql语句的实际应用：
已知考生表tdb_ks包含：考号 ,姓名,成绩字段
| id |
number |
name |
grade |
| 1 |
1001 |
小明 |
89 |
| 2 |
3001 |
小丽 |
90 |
| 3 |
2002 |
张三 |
88 |
1>写出新建考生表SQL语句，要求定义id为主键并且自动增长.
mysql> CREATE TABLE tdb_ks(
-> id int NOT NULL AUTO_INCREMENT PRIMARYKEY,
-> number int NOTNULL,
-> name varchar(50)NOT NULL,
-> grade int NOTNULL );
Query OK, 0 rows affected (0.03 sec)
mysql> DESC tdb_ks;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| number | int(11) |NO | | NULL | |
| name | varchar(50) |NO | | NULL | |
| grade | int(11) | NO | | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
2>向考生表添加记录
mysql> INSERT INTO tdb_ks (number,name,grade)VALUES(1001,'小明',89);
mysql> INSERT INTO tdb_ks (number,name,grade)VALUES(1002,'小丽',90);
mysql> INSERT INTO tdb_ks (number,name,grade)VALUES(1003,'张三',88);
mysql> INSERT INTO tdb_ks (number,name,grade)VALUES(1004,'李四',70);
3>查询考生信息
mysql> SELECT * FROM tdb_ks;
+----+--------+------+-------+
| id | number | name | grade |
+----+--------+------+-------+
| 1 | 1001 | 小明 | 89 |
| 2 | 1002 | 小丽 | 90 |
| 3 | 1003 | 张三 | 100 |
| 4 | 1004 | 李四 | 70 |
+----+--------+------+-------+
4>根据姓名更改考生信息
mysql> UPDATE tdb_ks SET grade = 100 WHERE name = '张三';
mysql> SELECT * FROM tdb_ks;
+----+--------+------+-------+
| id | number | name | grade |
+----+--------+------+-------+
| 1 | 1001 | 小明 | 89 |
| 2 | 1002 | 小丽 | 90 |
| 3 | 1003 | 张三 | 100 |
| 4 | 1004 | 李四 | 70 |
5>根据考号删除考生
mysql> DELETE FROM tdb_ks WHERE number = 1004;
mysql> SELECT * FROM tdb_ks;
+----+--------+------+-------+
| id | number | name | grade |
+----+--------+------+-------+
| 1 | 1001 | 小明 | 89 |
| 2 | 1002 | 小丽 | 90 |
| 3 | 1003 | 张三 | 100 |
+----+--------+------+-------+
6>查询所有学生总成绩
mysql> SELECTSUM(grade) AS 总成绩 FROM tdb_ks;
+--------+
| 总成绩 |
+--------+
| 279 |
+--------+
7>查询高于平均分的所有学生
mysql> SELECTROUND(AVG(grade)) AS 平均分 FROM tdb_ks;
+--------+
| 平均分 |
+--------+
| 93 |
+--------+
mysql> SELECT *FROM tdb_ks WHERE grade > (SELECT AVG(grade) FROM tdb_ks);
+----+--------+------+-------+
| id | number | name| grade |
+----+--------+------+-------+
| 3 | 1003 | 张三 | 100 |
+----+--------+------+-------+
1. 假下有一张订单表信息如下:
| id |
order_date |
Order_price |
customer_name |
| 1 |
2008/12/29 |
1000 |
布鲁斯 |
| 2 |
2008/11/23 |
1600 |
卡特 |
| 3 |
2008/10/05 |
700 |
布鲁斯 |
| 4 |
2008/09/28 |
500 |
布鲁斯 |
| 5 |
2008/08/06 |
2100 |
安迪 |
| 6 |
2008/07/21 |
100 |
卡特 |
1>查询客户布鲁斯订单总金额.
mysql>SELECT custmer, SUM(order_price) FROM orders GROUP BY custmer HAVING custmer ='bush';
+---------+------------------+
|custmer | SUM(order_price) |
+---------+------------------+
|bush | 2850 |
+---------+------------------+
1 rowin set (0.01 sec)
2>查询订单总金额在1800到3000间的客户
mysql>SELECT custmer,SUM(order_price) FROM orders GROUP BY custmer HAVINGSUM(order_price) BETWEEN 1800 AND 3000;
+---------+------------------+
|custmer | SUM(order_price) |
+---------+------------------+
|adams | 2000 |
|bush | 2850 |
+---------+------------------+
4. 有如下职工表
.
1>查找麻主管的直接领导
mysql>SELECT * FROM people;
+----+--------+-----------+
| id| name | parent_id |
+----+--------+-----------+
| 1 | 范总 | 0 |
| 2 | 何经理 | 1 |
| 3 | 麻主管 | 2 |
| 4 | 刘主管 | 2 |
| 5 | 李高级 | 3 |
| 6 | 王中级 | 3 |
| 7 | 张初级 | 4 |
+----+--------+-----------+
7rows in set (0.02 sec)
mysql>SELECT s.name AS 员工, f.name AS领导 FROM people AS s
-> INNER JOIN people AS f
-> ON s.parent_id = f.id
-> AND s.name = '麻主管';
+--------+--------+
| 员工 |领导 |
+--------+--------+
| 麻主管 |何经理 |
+--------+--------+
1 rowin set (0.00 sec)
3.查询总金额小于2000的人：
Select customer_name,SUM(Order_price) FROM orders GROUP BY customer_name HAVINGSUM(order_price)<2000;