mysql基础查询
查询方法
本文查询操作只涉及到一个学生信息表， 如下
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+-------+--------+-------+
入门级查询
查询一列
语法为 select columu_name from table_name; 任何查询语句都以逗号冒号结尾
mysql> select s_name from students;
+--------+
| s_name |
+--------+
| 曾华 |
| 匡明 |
| 王丽 |
| 李军 |
| 王芳 |
| 陆军 |
| 王尼玛 |
| 张全蛋 |
| 赵铁柱 |
查询多列
不同列之间用英文逗号隔开
mysql> select s_num, s_name, s_birthday from students;
+-------+--------+---------------------+
| s_num | s_name | s_birthday |
+-------+--------+---------------------+
| 101 | 曾华 | 1977-09-01 00:00:00 |
| 102 | 匡明 | 1975-10-02 00:00:00 |
| 103 | 王丽 | 1976-01-23 00:00:00 |
| 104 | 李军 | 1976-02-20 00:00:00 |
| 105 | 王芳 | 1975-02-10 00:00:00 |
| 106 | 陆军 | 1974-06-03 00:00:00 |
| 107 | 王尼玛 | 1976-02-20 00:00:00 |
| 108 | 张全蛋 | 1975-02-10 00:00:00 |
| 109 | 赵铁柱 | 1974-06-03 00:00:00 |
+-------+--------+---------------------+
查询全部列
* 表示全选
mysql> select * from students;
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+-------+--------+-------+---------------------+---------+
查询不重复的值
distinct 去掉重复值
mysql> select distinct s_class from students;
+---------+
| s_class |
+---------+
| 95033 |
| 95031 |
+---------+
查询前n行
mysql> select * from students limit 5;
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
+-------+--------+-------+---------------------+---------+
查询从某行开始的n行
语法 limit length offset start;
mysql> select * from students limit 5 offset 3; --从第三行开始取五行--
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
+-------+--------+-------+---------------------+---------+
排序
单一字段排序
mysql> select * from students order by s_num; --按照s_num 升序 默认升序--
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+-------+--------+-------+---------------------+---------+
多字段排序
多个排序字段用逗号隔开
mysql> select * from students order by s_class ,s_sex; --先按班级升序，班级相同再按性别升序
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
+-------+--------+-------+---------------------+---------+
降序
DESC (descending ;降序排列 ，以此递减）
ASC (ascending ; 上行,递增,升序）默认
mysql> select * from students order by s_num desc;
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
+-------+--------+-------+---------------------+---------+
混合字段排序
mysql> select * from students order by s_class ASC ,s_sex DESC; --先按班级升序 ，相同按性别降序
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
+-------+--------+-------+---------------------+---------+
where条件查询
算术运算符
可以对查询结果经行 + - * /四则运算
mysql> select 2*s_num from students; --输出2倍学号--
+---------+
| 2*s_num |
+---------+
| 202 |
| 204 |
| 206 |
| 208 |
| 210 |
| 212 |
| 214 |
| 216 |
| 218 |
+---------+
关系运算符
关系运算符包括大于 > , 大于等于 >= ,小于< 等等
mysql> select * from students where s_num > 107; --where 表示当 --
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+-------+--------+-------+---------------------+---------+
逻辑运算符
逻辑运算符与其他编程语言都类似， 分别为 并 and , 或 or , 非 not .
mysql> select * from students where s_num > 105 and s_class = '95033'; -- 同时成立 and--
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
+-------+--------+-------+---------------------+---------+
mysql> select * from students where s_num > 105 or s_class = '95033'; -- 有一个成立 or--
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+-------+--------+-------+---------------------+---------+
mysql> select * from students where not s_sex ='男'; -- 否定之后的条件 not--
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
+-------+--------+-------+---------------------+---------+
区间between and
连续区间内取值可以用 between and ,离散的取值可以用 in
mysql> select * from students where s_num between 104 and 107 ; -- 两边都包含， 相当于闭区间--
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
列举 in
mysql> select * from students where s_name in ('李军','王尼玛'); --括号--
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
+-------+--------+-------+---------------------+---------+
空值查询
IS NULL 查询空值
mysql> insert into students(s_num, s_name, s_sex) values('110','刘表','男');
Query OK, 1 row affected (0.01 sec)
mysql> select * from students; -- 插入一条数据，其s_birthday，s_class为空--
+-------+--------+-------+---------------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
| 110 | 刘表 | 男 | NULL | NULL |
+-------+--------+-------+---------------------+---------+
mysql> select * from students where s_birthday IS NULL;
+-------+--------+-------+------------+---------+
| s_num | s_name | s_sex | s_birthday | s_class |
+-------+--------+-------+------------+---------+
| 110 | 刘表 | 男 | NULL | NULL |
+-------+--------+-------+------------+---------+
分组
group by 分组
mysql> select count(*),s_class from students group by s_class; --count() 计数函数--
+----------+---------+
| count(*) | s_class |
+----------+---------+
| 4 | 95033 |
| 5 | 95031 |
| 1 | NULL |
+----------+---------+
3 rows in set (0.00 sec)
本文是mysql最基本的查询语句，每条只有一个方法，旨在掌握透彻基础，在复杂的查询不会轻易写错 。