MySQL查询交集、并集、差集
背景和使用的数据样本
该章节学些主要涉及到Datawhale SQL 组队学习任务；
本次使用的数据，由Datawhale 开源提供，具体代码见文章尾部：各位看官可以直接复制到MySQL Workbench 上运行生成数据库和表格。
MySQL WorkBench 如何对数据进行我们常见的集合运算呢？
Union、 INTERSECT（遗憾的是MySQL 8.0 不支持该运算用where /in 实现）、EXCEPT（遗憾的是MySQL 8.0 不支持该运算，但巧妙的用where …Not in 实现），本博客日记主要记录一些注意事项。
那么MySQL如何处理交集和差集呢？
基本语法
Select <列名1>,<列名2>,<列名3>... from <表名>
union -- 或者其他 intersect、except、union all等）
Select <列名1>,<列名2>,<列名3>... from <表名>
注意事项
1.首先：任何执行Union、 INTERSECT、EXCEPT的语句
都要注意，该关键字前后的Select 语句中选择的列的数量要一致，不一致会提示错误：
select product_id, product_name -- 注意这里是2选择查询两个列
from product
union
select product_id, product_name -- 这里的列的数量要与前面的列的数量一致
from product2;
正确的代码输出结果如下：
其次，select 语句中列数量不一致时，提示：
Error Code: 1222. The used SELECT statements have a different number of columns 0.000 sec
但是，对于select 中的选择的可以不一定是表格中原来就有的列表，此时能够正常查询数据表，具体如下：
select product_id, product_name
from product
union
select product_id, '1'
from product2;
结果如下：
2.Union vs Union All 的区别
Union 操作，自动去重复，即两个或多个数据表中相同的行只吃出现一次；
若想要所有表中的对应的数据都显示的话，则需要用到Union all
3.select sysdate() ; 查询返回系统当前的时间；
select product_name, sale_price, purchase_price
from product
union
select sysdate(), sysdate() , sysdate()
from product;
查询结果如下：
**4.MySQL 8.0 不支持交运算INTERSECT、except **
5. 查询差集：
-- 使用 IN 子句的实现方法
SELECT *
FROM product
WHERE product_id NOT IN (SELECT product_id
FROM product2)
结果：
CREATE DATABASE `shop` ;
USE `shop`;
DROP TABLE IF EXISTS `chars`;
CREATE TABLE `chars` (
`chr` char(3) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
PRIMARY KEY (`chr`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
insert into `chars`(`chr`) values ('1'),('10'),('11'),('2'),('222'),('3');
DROP TABLE IF EXISTS `empskills`;
CREATE TABLE `empskills` (
`emp` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`skill` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
PRIMARY KEY (`emp`,`skill`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
insert into `empskills`(`emp`,`skill`) values ('平井','C++'),('平井','oracle'),('平井','perl'),('平井','php'),('平井','Unix'),('渡来','Oracle'),('相田','C#'),('相田','Java'),('相田','Oracle'),('相田','UNIX'),('神崎','Java'),('神崎','Oracle'),('神崎','UNIX'),('若田部','Perl');
DROP TABLE IF EXISTS `inventoryproduct`;
CREATE TABLE `inventoryproduct` (
`inventory_id` char(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_id` char(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`inventory_quantity` int NOT NULL,
PRIMARY KEY (`inventory_id`,`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
insert into `inventoryproduct`(`inventory_id`,`product_id`,`inventory_quantity`) values ('P001','0001',0),('P001','0002',120),('P001','0003',200),('P001','0004',3),('P001','0005',0),('P001','0006',99),('P001','0007',999),('P001','0008',200),('P002','0001',10),('P002','0002',25),('P002','0003',34),('P002','0004',19),('P002','0005',99),('P002','0006',0),('P002','0007',0),('P002','0008',18);
DROP TABLE IF EXISTS `product`;
CREATE TABLE `product` (
`product_id` char(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_name` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_type` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`sale_price` int DEFAULT NULL,
`purchase_price` int DEFAULT NULL,
`regist_date` date DEFAULT NULL,
PRIMARY KEY (`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
insert into `product`(`product_id`,`product_name`,`product_type`,`sale_price`,`purchase_price`,`regist_date`) values ('0001','T恤','衣服',1000,500,'2009-09-20'),('0002','打孔器','办公用品',500,320,'2009-09-11'),('0003','运动T恤','衣服',4000,2800,NULL),('0004','菜刀','厨房用具',3000,2800,'2009-09-20'),('0005','高压锅','厨房用具',6800,5000,'2009-01-15'),('0006','叉子','厨房用具',500,NULL,'2009-09-20'),('0007','擦菜板','厨房用具',880,790,'2008-04-28'),('0008','圆珠笔','办公用品',100,NULL,'2009-11-11');
DROP TABLE IF EXISTS `product2`;
CREATE TABLE `product2` (
`product_id` char(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_name` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_type` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`sale_price` int DEFAULT NULL,
`purchase_price` int DEFAULT NULL,
`regist_date` date DEFAULT NULL,
PRIMARY KEY (`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
insert into `product2`(`product_id`,`product_name`,`product_type`,`sale_price`,`purchase_price`,`regist_date`) values ('0001','T恤','衣服',1000,500,'2009-09-20'),('0002','打孔器','办公用品',500,320,'2009-09-11'),('0003','运动T恤','衣服',4000,2800,NULL),('0009','手套','衣服',800,500,NULL),('0010','水壶','厨房用具',2000,1700,'2009-09-20');
DROP TABLE IF EXISTS `productcopy`;
CREATE TABLE `productcopy` (
`product_id` char(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_name` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_type` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`sale_price` int DEFAULT NULL,
`purchase_price` int DEFAULT NULL,
`regist_date` date DEFAULT NULL,
PRIMARY KEY (`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
DROP TABLE IF EXISTS `productins`;
CREATE TABLE `productins` (
`product_id` char(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_name` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_type` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`sale_price` int DEFAULT '0',
`purchase_date` int DEFAULT NULL,
`regist_date` date DEFAULT NULL,
PRIMARY KEY (`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
DROP TABLE IF EXISTS `producttype`;
CREATE TABLE `producttype` (
`product_type` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`sum_sale_price` int DEFAULT NULL,
`sum_purchase_price` int DEFAULT NULL,
PRIMARY KEY (`product_type`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
DROP TABLE IF EXISTS `samplelike`;
CREATE TABLE `samplelike` (
`strcol` varchar(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
PRIMARY KEY (`strcol`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
insert into `samplelike`(`strcol`) values ('abcdd'),('abcddd'),('abddc'),('abdddc'),('ddabc'),('dddabc');
DROP TABLE IF EXISTS `samplemath`;
CREATE TABLE `samplemath` (
`m` decimal(10,3) DEFAULT NULL,
`n` int DEFAULT NULL,
`p` int DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
insert into `samplemath`(`m`,`n`,`p`) values ('500.000',0,NULL),('-180.000',0,NULL),(NULL,NULL,NULL),(NULL,7,3),(NULL,5,2),(NULL,4,NULL),('8.000',NULL,3),('2.270',1,NULL),('5.555',2,NULL),(NULL,1,NULL),('8.760',NULL,NULL);
DROP TABLE IF EXISTS `samplestr`;
CREATE TABLE `samplestr` (
`str1` varchar(40) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL,
`str2` varchar(40) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL,
`str3` varchar(40) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
insert into `samplestr`(`str1`,`str2`,`str3`) values ('opx','rt',NULL),('abc','def',NULL),('山田','太郎','是我'),('aaa',NULL,NULL),(NULL,'xyz',NULL),('@!#$%',NULL,NULL),('ABC',NULL,NULL),('aBC',NULL,NULL),('abc太郎','abc','ABC'),('abcdefabc','abc','ABC'),('micmic','i','I');
DROP TABLE IF EXISTS `shopproduct`;
CREATE TABLE `shopproduct` (
`shop_id` char(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`shop_name` varchar(200) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`product_id` char(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
`quantity` int NOT NULL,
PRIMARY KEY (`shop_id`,`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
insert into `shopproduct`(`shop_id`,`shop_name`,`product_id`,`quantity`) values ('000A','东京','0001',30),('000A','东京','0002',50),('000A','东京','0003',15),('000B','名古屋','0002',30),('000B','名古屋','0003',120),('000B','名古屋','0004',20),('000B','名古屋','0006',10),('000B','名古屋','0007',40),('000C','大阪','0003',20),('000C','大阪','0004',50),('000C','大阪','0006',90),('000C','大阪','0007',70),('000D','福冈','0001',100);
DROP TABLE IF EXISTS `skills`;
CREATE TABLE `skills` (
`skill` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,
PRIMARY KEY (`skill`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
insert into `skills`(`skill`) values ('Java'),('Oracle'),('UNIX');
总结
以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。
