Union和Union All区别

Union：对两个结果集进行并集操作，不包括重复行，同时进行默认规则的排序；
Union All：对两个结果集进行并集操作，包括重复行，不进行排序；

1.创建表​​​​

Create table Table1(  
    id int not null,  
    name varchar(20) not null  
)；

Create table Table2(  
    id int not null,  
    name varchar(20) not null  
)；

2.插入测试数据

Insert into Table1 values (1,'heshuyu');
Insert into Table1 values (2,'zhangsan');
Insert into Table1 values (3,'lisi');

Insert into Table2 values (1,'heshuyu');  
Insert into Table2 values (2,'liudehua');
Insert into Table2 values (3,'zhangchao'); 
Insert into Table2 values (4,'zhangxueyou');

3.查看表

mysql> select * from Table1;
+----+----------+
| id | name     |
+----+----------+
|  1 | heshuyu  |
|  2 | zhangsan |
|  3 | lisi     |
+----+----------+
3 rows in set (0.00 sec)

mysql> select * from Table2;
+----+-------------+
| id | name        |
+----+-------------+
|  1 | heshuyu     |
|  2 | liudehua    |
|  3 | zhangchao   |
|  4 | zhangxueyou |
+----+-------------+
4 rows in set (0.00 sec)

4.Union查询​

mysql> select * from Table1 union select * from Table2;
+----+-------------+
| id | name        |
+----+-------------+
|  1 | heshuyu     |
|  2 | zhangsan    |
|  3 | lisi        |
|  2 | liudehua    |
|  3 | zhangchao   |
|  4 | zhangxueyou |
+----+-------------+
6 rows in set (0.00 sec)

5.Union ALL查询​​​

mysql> select * from Table1 union all select * from Table2;
+----+-------------+
| id | name        |
+----+-------------+
|  1 | heshuyu     |
|  2 | zhangsan    |
|  3 | lisi        |
|  1 | heshuyu     |
|  2 | liudehua    |
|  3 | zhangchao   |
|  4 | zhangxueyou |
+----+-------------+
7 rows in set (0.00 sec)

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MYSQL