MySQL增删查改 练习(基础)

Posted 2022-04-27 Perceus

@TOC

---

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)

把一个表里面的所有行和所有列都查找出到，查找的结果是一个“临时表”，之前我们说的 数据库 的表都是在硬盘上的，而此处的这个查询结果 临时表 ，不是在硬盘上，而是在内存中，随着进行了输出之后，数据也就被释放了~
注意：

---

指定列查询

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

-- 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

-- 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

在 selcet 的后面加上一个where 字句，后面跟上一个具体的筛选条件
语法;select 列名 from 表名 where 条件;

1. where条件可以使用表达式,但是不能使用别名
2. 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

此处这里的孙%就能匹配到任意 孙 开头的字符串,其他的类型于这样的名字也能匹配到.
比如: 孙 ,或者 孙sadsadasda
但是类似于 这种就匹配不到:aaa孙aaa,bbb孙

-- % 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

注意:这里 比较 NULL 是不能用 = 的, = 是无法比较的,结果是 假,如果要比较空 只能用 <=> 比较

或者 这样写 也可以

-- 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 0-3
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 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)

---