MySQL 8.0.31 集合操作INTERSECT和EXCEPT

news2024/11/15 17:53:30

对于聚合的功能MySQL是都是默默的发展。在最新的8.0.31版本中提供对集合操作INTERSECT和EXCEPT。这样一来，集合操作功能基本圆满了。MySQL5.7.40版本是不支持这个集合的。

In this release MySQL adds support for the SQL standard INTERSECT and EXCEPT table operators.
query_a INTERSECT query_b includes only rows appearing in both result sets.
query_a EXCEPT query_b returns any rows from the result set of query_a which are not in the result of query_b.
INTERSECT and EXCEPT both support DISTINCT and ALL, with DISTINCT the default in both cases. (This is the same as for UNION).
INTERSECT groups before EXCEPT or UNION, so TABLE r EXCEPT TABLE s INTERSECT TABLE t is evaluated as TABLE r EXCEPT (TABLE s INTERSECT TABLE t).
See INTERSECT Clause, and EXCEPT Clause, for additional information and examples. (Bug #1309, Bug #31336, Bug #11747209, Bug #11744757)

目前MySQL里提供的集合操作包含：【UNION ，UNION ALL，INTERSECT，EXCEPT】

集合类型	数据	结果
UNION ALL	A={1,2,3}，B={3,4,5,6}	ALL={1,2,3,3,4,5,6}
UNION	A={1,2,3}，B={3,4,5,6}	AUB={1,2,3,4,5,6}
INTERSECT	A={1,2,3}，B={3,4,5,6}	A∩B={3}
EXCEPT	A={1,2,3}，B={3,4,5,6}	A-B={1,2}

集合

测试集合

CREATE TABLE `DataSetA` (
  `id` bigint NOT NULL ,
  `name` varchar(10) DEFAULT NULL
);
INSERT INTO DataSetA(id,name) VALUES(1,'A'),(2,'A'),(3,'C');

CREATE TABLE `DataSetB` (
  `id` bigint NOT NULL ,
  `name` varchar(10) DEFAULT NULL
);
INSERT INTO DataSetB(id,name) VALUES(3,'C'),(4,'D'),(5,'E'),(6,'F');

CREATE TABLE `DataSetC` (
  `id` bigint NOT NULL, 
  `name` varchar(10) DEFAULT NULL
);
INSERT INTO DataSetC(id,name) VALUES(6,'F'),(7,'G'),(7,'G'),(8,'H');

不同的结果操作集：

执行计划：

除了UNION ALL，都需要通过Using temporary 进行运算，所以性能还是存在一定影响。毕竟涉及临时表。

集合中的DISTINCT和ALL

INTERSECT和EXCEPT都支持DISTINCT和ALL与UNION相同)，在这两种情况下默认为DISTINCT。
字面意义相同是否去重或全部显示。

uery_block INTERSECT [ALL | DISTINCT] query_block
mysql> table  DataSetC INTERSECT DISTINCT table DataSetC;
+----+------+
| id | name |
+----+------+
|  6 | F    |
|  7 | G    |
|  8 | H    |
+----+------+
3 rows in set (0.00 sec)

mysql> table  DataSetC INTERSECT ALL table DataSetC;
+----+------+
| id | name |
+----+------+
|  6 | F    |
|  7 | G    |
|  7 | G    |
|  8 | H    |
+----+------+
4 rows in set (0.00 sec)
复制
备注：对于INTERSECT ALL，左手表中任何唯一行的最大支持的重复数是4294967295。

注意事项

从底层实现和测试现象来看，集合对比方式是用object方式进行对比。只要列数量对就可以。类型无关紧要。但实际业务中肯定是满足字段，类型一致。

1.集合对比必须具有相同的列数，列数不同出现问题:

mysql> SELECT ID FROM DataSetA 
       INTERSECT 
     SELECT ID ,NAME FROM DataSetB;
ERROR 1222 (21000): The used SELECT statements have a different number of columns

2. 不同类型对比，可以进行对比。但对于最终结果来说就没意义。

mysql> SELECT ID FROM DataSetA  
       UNION  
       SELECT NAME FROM DataSetA;
+------+
| ID   |
+------+
| 1    |
| 2    |
| 3    |
| A    |
| C    |
+------+
5 rows in set (0.00 sec)

3.版本对比写法不同
MySQL 5.7相比,在MySQL 8.0中，对SELECT和集合的解析器规则进行了重构，使其更加一致并减少了重复.

LIMIT 写法

#mysql5.7.40不支持
mysql> (SELECT 1 AS result UNION SELECT 2) LIMIT 1;
ERROR 1064 (42000): You have an error in your SQL syntax; 
check the manual that corresponds to your MySQL server version for the right 
syntax to use near 'UNION SELECT 2) LIMIT 1' at line 1

#mysql8.0.31支持
mysql> (SELECT 1 AS result UNION SELECT 2) LIMIT 1;
+--------+
| result |
+--------+
|      1 |
+--------+
1 row in set (0.00 sec)

FOR UPDATE 写法

#mysql5.7.40
mysql> SELECT 1 FOR UPDATE UNION SELECT 1 FOR UPDATE;
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

mysql> (SELECT 1 FOR UPDATE) UNION (SELECT 1 FOR UPDATE);
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

#mysql8.0.31 更严谨
mysql> SELECT 1 FOR UPDATE UNION SELECT 1 FOR UPDATE;
ERROR 1064 (42000): You have an error in your SQL syntax; 
check the manual that corresponds to your MySQL server version for the right 
syntax to use near 'UNION SELECT 1 FOR UPDATE' at line 1
mysql> (SELECT 1 FOR UPDATE) UNION (SELECT 1 FOR UPDATE);
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)