文章目录
增加
建表
mysql> create database test_exam;
Query OK, 1 row affected (0.00 sec)
mysql> use test_exam;
Database changed
mysql> create table exam (
-> id int,
-> name varchar(20),
-> chinese decimal(3,1),
-> math decimal(3,1),
-> english decimal(3,1)
-> );
Query OK, 0 rows affected (0.02 sec)
多行数据 全列插入
mysql> insert into exam values
-> (1, '刘备', 90.1, 70.3, 40.9),
-> (2, '关羽', 90.1, 60.3, 30.8),
-> (3, '大乔', 99, 70.3, 30.8),
-> (4, '吕布', 80.5, 50.3, 70.2),
-> (5, '貂蝉', 80.5, 87.6, 90.3),
-> (6, '孙尚香', 99, 12.1, 10),
-> (7, '小乔', 98, 99, 4.3),
-> (8, '孙权', 85, 77, 87);
Query OK, 8 rows affected (0.01 sec)
Records: 8 Duplicates: 0 Warnings: 0
多行数据 指定列插入
mysql> insert into exam (id, name) values (9, '孙策'), (10, '刘禅');
Query OK, 2 rows affected (0.01 sec)
Records: 2 Duplicates: 0 Warnings: 0
查询
全列查询
- 注意:这种方式只限测试方式查询,千万不能再生产环境上的服务器执行这样的sql
mysql> select * from exam;
+------+-----------+---------+------+---------+
| id | name | chinese | math | english |
+------+-----------+---------+------+---------+
| 1 | 刘备 | 90.1 | 70.3 | 40.9 |
| 2 | 关羽 | 90.1 | 60.3 | 30.8 |
| 3 | 大乔 | 99.0 | 70.3 | 30.8 |
| 4 | 吕布 | 80.5 | 50.3 | 70.2 |
| 5 | 貂蝉 | 80.5 | 87.6 | 90.3 |
| 6 | 孙尚香 | 99.0 | 12.1 | 10.0 |
| 7 | 小乔 | 98.0 | 99.0 | 4.3 |
| 8 | 孙权 | 85.0 | 77.0 | 87.0 |
| 9 | 孙策 | NULL | NULL | NULL |
| 10 | 刘禅 | NULL | NULL | NULL |
+------+-----------+---------+------+---------+
10 rows in set (0.00 sec)
指定列查询
mysql> select id,name from exam;
+------+-----------+
| id | name |
+------+-----------+
| 1 | 刘备 |
| 2 | 关羽 |
| 3 | 大乔 |
| 4 | 吕布 |
| 5 | 貂蝉 |
| 6 | 孙尚香 |
| 7 | 小乔 |
| 8 | 孙权 |
| 9 | 孙策 |
| 10 | 刘禅 |
+------+-----------+
10 rows in set (0.00 sec)
查询字段为表达式
mysql> select id, name, english + 10 from exam;
+------+-----------+--------------+
| id | name | english + 10 |
+------+-----------+--------------+
| 1 | 刘备 | 50.9 |
| 2 | 关羽 | 40.8 |
| 3 | 大乔 | 40.8 |
| 4 | 吕布 | 80.2 |
| 5 | 貂蝉 | 100.3 |
| 6 | 孙尚香 | 20.0 |
| 7 | 小乔 | 14.3 |
| 8 | 孙权 | 97.0 |
| 9 | 孙策 | NULL |
| 10 | 刘禅 | NULL |
+------+-----------+--------------+
10 rows in set (0.00 sec)
mysql> select id, name, chinese + math + english from exam;
+------+-----------+--------------------------+
| id | name | chinese + math + english |
+------+-----------+--------------------------+
| 1 | 刘备 | 201.3 |
| 2 | 关羽 | 181.2 |
| 3 | 大乔 | 200.1 |
| 4 | 吕布 | 201.0 |
| 5 | 貂蝉 | 258.4 |
| 6 | 孙尚香 | 121.1 |
| 7 | 小乔 | 201.3 |
| 8 | 孙权 | 249.0 |
| 9 | 孙策 | NULL |
| 10 | 刘禅 | NULL |
+------+-----------+--------------------------+
10 rows in set (0.00 sec)
查询字段 名字重定义
mysql> select id, name, chinese + math + english as totle from exam;
+------+-----------+-------+
| id | name | totle |
+------+-----------+-------+
| 1 | 刘备 | 201.3 |
| 2 | 关羽 | 181.2 |
| 3 | 大乔 | 200.1 |
| 4 | 吕布 | 201.0 |
| 5 | 貂蝉 | 258.4 |
| 6 | 孙尚香 | 121.1 |
| 7 | 小乔 | 201.3 |
| 8 | 孙权 | 249.0 |
| 9 | 孙策 | NULL |
| 10 | 刘禅 | NULL |
+------+-----------+-------+
10 rows in set (0.00 sec)
去重 distinct
- 使用去重distinct时,所有的列都必须放在distinct的后面
mysql> select distinct chinese from exam;
+---------+
| chinese |
+---------+
| 90.1 |
| 99.0 |
| 80.5 |
| 98.0 |
| 85.0 |
| NULL |
+---------+
6 rows in set (0.01 sec)
排序 order by
- asc为升序 desc为降序 什么都不加 默认asc
-- 查询同学及总分，由高到低
mysql> select id, name, chinese + math + english as totle from exam order by totle desc;
+------+-----------+-------+
| id | name | totle |
+------+-----------+-------+
| 5 | 貂蝉 | 258.4 |
| 8 | 孙权 | 249.0 |
| 1 | 刘备 | 201.3 |
| 7 | 小乔 | 201.3 |
| 4 | 吕布 | 201.0 |
| 3 | 大乔 | 200.1 |
| 2 | 关羽 | 181.2 |
| 6 | 孙尚香 | 121.1 |
| 9 | 孙策 | NULL |
| 10 | 刘禅 | NULL |
+------+-----------+-------+
10 rows in set (0.00 sec)
-- 查询同学各门成绩，依次按 数学降序，英语升序，语文升序的方式显示
mysql> select * from exam order by chinese desc, math desc, english desc;
+------+-----------+---------+------+---------+
| id | name | chinese | math | english |
+------+-----------+---------+------+---------+
| 3 | 大乔 | 99.0 | 70.3 | 30.8 |
| 6 | 孙尚香 | 99.0 | 12.1 | 10.0 |
| 7 | 小乔 | 98.0 | 99.0 | 4.3 |
| 1 | 刘备 | 90.1 | 70.3 | 40.9 |
| 2 | 关羽 | 90.1 | 60.3 | 30.8 |
| 8 | 孙权 | 85.0 | 77.0 | 87.0 |
| 5 | 貂蝉 | 80.5 | 87.6 | 90.3 |
| 4 | 吕布 | 80.5 | 50.3 | 70.2 |
| 9 | 孙策 | NULL | NULL | NULL |
| 10 | 刘禅 | NULL | NULL | NULL |
+------+-----------+---------+------+---------+
10 rows in set (0.00 sec)
条件查询
运算符
-
>, >=, <, <= 大于，大于等于，小于，小于等于 -
= 等于，NULL 不安全，例如 NULL = NULL 的结果是 NULL -
<=> 等于，NULL 安全，例如 NULL <=> NULL 的结果是 TRUE(1) -
!=, <> 不等于 -
BETWEEN a0 AND a1范围匹配，[a0, a1]，如果 a0 <= value <= a1，返回 TRUE(1) -
IN (option, ...) 如果是 option 中的任意一个，返回TRUE(1) -
IS NULL 是 NULL -
IS NOT NULL 不是 NULL -
LIKE模糊匹配 % 表示任意多个（包括 0 个）任意字符； _ 表示任意一个字符扫描二维码关注公众号，回复： 11277192 查看本文章
-
AND 多个条件必须都为 TRUE(1)，结果才是 TRUE(1) -
OR 任意一个条件为 TRUE(1), 结果为 TRUE(1) -
NOT 条件为 TRUE(1)，结果为 FALSE(0) -
注意:
- where条件可以使用表达式,但是不能使用别名
- and 的优先级高于 or 在同时使用时,需要使用小括号()包裹优先执行的部分
比较查询
-- 查询英语不及格的同学及英语成绩 ( < 60 )
mysql> select id, name, english from exam where english < 60;
+------+-----------+---------+
| id | name | english |
+------+-----------+---------+
| 1 | 刘备 | 40.9 |
| 2 | 关羽 | 30.8 |
| 3 | 大乔 | 30.8 |
| 6 | 孙尚香 | 10.0 |
| 7 | 小乔 | 4.3 |
+------+-----------+---------+
5 rows in set (0.00 sec)
-- 查询语文成绩好于英语成绩的同学
mysql> select id, name, chinese, english from exam where chinese > english;
+------+-----------+---------+---------+
| id | name | chinese | english |
+------+-----------+---------+---------+
| 1 | 刘备 | 90.1 | 40.9 |
| 2 | 关羽 | 90.1 | 30.8 |
| 3 | 大乔 | 99.0 | 30.8 |
| 4 | 吕布 | 80.5 | 70.2 |
| 6 | 孙尚香 | 99.0 | 10.0 |
| 7 | 小乔 | 98.0 | 4.3 |
+------+-----------+---------+---------+
6 rows in set (0.00 sec)
-- 查询总分在 200 分以下的同学
mysql> select id, name, chinese + math + english as totle from exam where chinese + math + english < 200;
+------+-----------+-------+
| id | name | totle |
+------+-----------+-------+
| 2 | 关羽 | 181.2 |
| 6 | 孙尚香 | 121.1 |
+------+-----------+-------+
2 rows in set (0.00 sec)
and与or
-- 查询语文成绩大于80分，且英语成绩大于80分的同学
mysql> select id, name, chinese, english from exam where chinese > 80 and english > 80;
+------+--------+---------+---------+
| id | name | chinese | english |
+------+--------+---------+---------+
| 5 | 貂蝉 | 80.5 | 90.3 |
| 8 | 孙权 | 85.0 | 87.0 |
+------+--------+---------+---------+
2 rows in set (0.00 sec)
-- 查询语文成绩大于80分，或英语成绩大于80分的同学
mysql> select id, name, chinese, english from exam where chinese > 80 or english > 80;
+------+-----------+---------+---------+
| id | name | chinese | english |
+------+-----------+---------+---------+
| 1 | 刘备 | 90.1 | 40.9 |
| 2 | 关羽 | 90.1 | 30.8 |
| 3 | 大乔 | 99.0 | 30.8 |
| 4 | 吕布 | 80.5 | 70.2 |
| 5 | 貂蝉 | 80.5 | 90.3 |
| 6 | 孙尚香 | 99.0 | 10.0 |
| 7 | 小乔 | 98.0 | 4.3 |
| 8 | 孙权 | 85.0 | 87.0 |
+------+-----------+---------+---------+
8 rows in set (0.00 sec)
范围查询
-- 查询语文成绩在 [80, 90] 分的同学及语文成绩
mysql> select id, name, chinese from exam where chinese between 80 and 90;
+------+--------+---------+
| id | name | chinese |
+------+--------+---------+
| 4 | 吕布 | 80.5 |
| 5 | 貂蝉 | 80.5 |
| 8 | 孙权 | 85.0 |
+------+--------+---------+
3 rows in set (0.00 sec)
in 查询
-- 查询数学成绩是 99.0 或者 60.3 或者 70.3 的同学及数学成绩
mysql> select name, math from exam where math in (99.0, 60.3, 70.3);
+--------+------+
| name | math |
+--------+------+
| 刘备 | 70.3 |
| 关羽 | 60.3 |
| 大乔 | 70.3 |
| 小乔 | 99.0 |
+--------+------+
4 rows in set (0.00 sec)
模糊查询 like
-- % 匹配任意多个（包括 0 个）字符
mysql> select id, name from exam where name like '孙%';
+------+-----------+
| id | name |
+------+-----------+
| 6 | 孙尚香 |
| 8 | 孙权 |
| 9 | 孙策 |
+------+-----------+
3 rows in set (0.00 sec)
-- _ 匹配严格的一个任意字符
mysql> select id, name from exam where name like '孙__';
+------+-----------+
| id | name |
+------+-----------+
| 6 | 孙尚香 |
+------+-----------+
1 row in set (0.00 sec)
mysql> select id, name from exam where name like '孙_';
+------+--------+
| id | name |
+------+--------+
| 8 | 孙权 |
| 9 | 孙策 |
+------+--------+
2 rows in set (0.00 sec)
-- 语文成绩以9开头并且姓为孙
mysql> select id, name, chinese from exam where name like '孙%' and chinese like '9%';
+------+-----------+---------+
| id | name | chinese |
+------+-----------+---------+
| 6 | 孙尚香 | 99.0 |
+------+-----------+---------+
1 row in set (0.00 sec)
null查询
-- 查成绩为null的同学
mysql> select id, name, chinese + math + english as totle from exam where chinese + math + english <=> null;
+------+--------+-------+
| id | name | totle |
+------+--------+-------+
| 9 | 孙策 | NULL |
| 10 | 刘禅 | NULL |
+------+--------+-------+
2 rows in set (0.00 sec)
分页查询
-- 查询成绩前三
mysql> select * from exam order by chinese + math + english desc limit 3;
+------+--------+---------+------+---------+
| id | name | chinese | math | english |
+------+--------+---------+------+---------+
| 5 | 貂蝉 | 80.5 | 87.6 | 90.3 |
| 8 | 孙权 | 85.0 | 77.0 | 87.0 |
| 1 | 刘备 | 90.1 | 70.3 | 40.9 |
+------+--------+---------+------+---------+
3 rows in set (0.00 sec)
-- 查询成绩4~6
-- offset 可以想成数组下标一样
mysql> select * from exam order by chinese + math + english desc limit 3 offset 3;
+------+--------+---------+------+---------+
| id | name | chinese | math | english |
+------+--------+---------+------+---------+
| 7 | 小乔 | 98.0 | 99.0 | 4.3 |
| 4 | 吕布 | 80.5 | 50.3 | 70.2 |
| 3 | 大乔 | 99.0 | 70.3 | 30.8 |
+------+--------+---------+------+---------+
3 rows in set (0.00 sec)
-- 查询 limit 或者 offset 过大也不会报错
mysql> select * from exam order by chinese + math + english desc limit 300 offset 300;
Empty set (0.00 sec)
修改
-- 将孙权同学的数学成绩变更为 80 分
-- Rows matched 表示where涉及到几行 Changed: 1表示改了几行 Warnings: 0表示出错多少
mysql> update exam set math = 80 where name = '孙权';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
-- 将总成绩倒数前三的 3 位同学的数学成绩加上 10 分
mysql> update exam set math = math + 10 order by chinese + math + english asc limit 3;
Query OK, 1 row affected (0.00 sec)
Rows matched: 3 Changed: 1 Warnings: 0
删除
-- 删除 刘备的成绩
mysql> delete from exam where name = '刘备';
Query OK, 1 row affected (0.01 sec)
-- 删除整张表的数据
mysql> delete from test_exam;
Query OK, 0 rows affected (0.00 sec)