单表查询

Posted 2020-11-22 wom1999

1：简单查询

SELECT语句

 

 

 

 

 

 1.1：查询所有字段

 

 

 

 eg1：查询student表中的所有的记录

创建一个student数据表

mysql> USE itcast;
Database changed

mysql> CREATE TABLE student(id INT(3) PRIMARY KEY AUTO_INCREMENT,name VARCHAR(20) NOT NULL,grade FLOAT,gender CHAR(2));
Query OK, 0 rows affected

用INSERT语句插入数据

mysql> INSERT INTO student(name,grade,gender) VALUES(‘wangwu‘,40,‘na‘),(‘zhangsan‘,100,‘nv‘),(‘qingming‘,90,‘na‘),(‘yuying‘,89,‘na‘),(‘zhansa‘,60,‘nv‘),(‘youqian‘,77,‘na‘);
Query OK, 6 rows affected
Records: 6  Duplicates: 0  Warnings: 4

查询数据

mysql> SELECT id,name,grade,gender FROM student;

+----+----------+-------+--------+
| id | name     | grade | gender |
+----+----------+-------+--------+
|  1 | wangwu   |    40 | na     |
|  2 | zhangsan |   100 | nv     |
|  3 | qingming |    90 | na     |
|  4 | yuying   |    89 | na     |
|  5 | zhansa   |    60 | nv     |
|  6 | youqian  |    77 | na     |
+----+----------+-------+--------+
6 rows in set

 

 例如：把name换到最后

mysql> SELECT id,grade,gender,name FROM student;

+----+-------+--------+----------+
| id | grade | gender | name     |
+----+-------+--------+----------+
|  1 |    40 | na     | wangwu   |
|  2 |   100 | nv     | zhangsan |
|  3 |    90 | na     | qingming |
|  4 |    89 | na     | yuying   |
|  5 |    60 | nv     | zhansa   |
|  6 |    77 | na     | youqian  |
+----+-------+--------+----------+
6 rows in set

 

 

 

 例如：用SELECT *FROM 查询student表中的数据

mysql> SELECT * FROM student;

+----+----------+-------+--------+
| id | name     | grade | gender |
+----+----------+-------+--------+
|  1 | wangwu   |    40 | na     |
|  2 | zhangsan |   100 | nv     |
|  3 | qingming |    90 | na     |
|  4 | yuying   |    89 | na     |
|  5 | zhansa   |    60 | nv     |
|  6 | youqian  |    77 | na     |
+----+----------+-------+--------+
6 rows in set

 1.2：查询指定字段

 

 eg2：

 

 查询结果

mysql> SELECT name,gender FROM student;
+----------+--------+
| name     | gender |
+----------+--------+
| wangwu   | na     |
| zhangsan | nv     |
| qingming | na     |
| yuying   | na     |
| zhansa   | nv     |
| youqian  | na     |
+----------+--------+
6 rows in set

注意：改变字段位置，所显示的结果位置也会改变，

例如：改变name和gender的位置

mysql> SELECT gender,name FROM student;

+--------+----------+
| gender | name     |
+--------+----------+
| na     | wangwu   |
| nv     | zhangsan |
| na     | qingming |
| na     | yuying   |
| nv     | zhansa   |
| na     | youqian  |
+--------+----------+
6 rows in set

2：按条件查询

2.1：关系运算符的查询

 

 常见关系运算符有：

 

 例如：查询student表中id=4的学生的姓名

mysql> SELECT id,name FROM student WHERE id=4;

+----+--------+
| id | name   |
+----+--------+
|  4 | yuying |
+----+--------+
1 row in set

例如：查询name为“wangwu”的学生的性别

mysql> SELECT name,gender FROM student WHERE name=‘wangwu‘;

+--------+--------+
| name   | gender |
+--------+--------+
| wangwu | na     |
+--------+--------+
1 row in set

例如：查询表中grade大于80的学生姓名

mysql> SELECT name FROM student WHERE grade>80;

+----------+
| name     |
+----------+
| zhangsan |
| qingming |
| yuying   |
+----------+
3 rows in set

2.2：带IN关键字的查询

 

 

例如：查询表中id为1 2 3的记录

mysql> SELECT id,grade,name,gender FROM student WHERE id IN(1,2,3);

+----+-------+----------+--------+
| id | grade | name     | gender |
+----+-------+----------+--------+
|  1 |    40 | wangwu   | na     |
|  2 |   100 | zhangsan | nv     |
|  3 |    90 | qingming | na     |
+----+-------+----------+--------+
3 rows in set

例如：查询表中id不为1 2 3的记录

mysql> SELECT id,grade,name,gender FROM student WHERE id NOT IN(1,2,3);

+----+-------+---------+--------+
| id | grade | name    | gender |
+----+-------+---------+--------+
|  4 |    89 | yuying  | na     |
|  5 |    60 | zhansa  | nv     |
|  6 |    77 | youqian | na     |
+----+-------+---------+--------+
3 rows in set

2.3：带BETWEEN　AND关键字的查询

 

 

 例如：查询表中ｉｄ在２－５之间的学生姓名

mysql> SELECT id,name FROM student WHERE id BETWEEN 2 AND 5;

+----+----------+
| id | name     |
+----+----------+
|  2 | zhangsan |
|  3 | qingming |
|  4 | yuying   |
|  5 | zhansa   |
+----+----------+
4 rows in set

 例如：查询表中ｉｄ不在２－５之间的学生姓名

mysql> SELECT id,name FROM student WHERE id NOT BETWEEN 2 AND 5;

+----+---------+
| id | name    |
+----+---------+
|  1 | wangwu  |
|  6 | youqian |
+----+---------+
2 rows in set