Question

我正在从事高中项目我想为用户运行查询以使用多个类别搜索药物这是ddl，

Create table medicine (
  MedId int(11) NOT NULL AUTO_INCREMENT,
  Name varchar(30) COLLATE utf8_bin DEFAULT NULL,
  Vendor varchar(20) COLLATE utf8_bin DEFAULT NULL,
  Quantity int(11) NOT NULL,
  type text COLLATE utf8_bin NOT NULL,
  price int(11) NOT NULL,
  PRIMARY KEY (MedId)
); 

create table category(
 CatId smallint auto_increment,
 Name varchar (20),
 primary key(CatID)
);

create table MedicineCat(
MedId int,
CatId smallint,
    foreign key (MedId) references medicine(MedId),
    foreign key (CatId) references category(CatId),
    primary key(MedId,CatId)


    );


SELECT medicinecat.MedID AS 'MedId', medicine.Name AS 'Name', medicine.price AS 'Price', medicine.Quantity AS 'Quantity'
FROM medicinecat
JOIN medicine ON medicine.MedId = medicinecat.MedId
WHERE CatId in (1,2,3);

我得到的是所有至少有一种类别的药物，我知道这是因为IN条款，我想要的是选择“所有类别”不属于该类别的药物。

Answer 1

select
    m.MedID AS 'MedId',
    m.Name AS 'Name',
    m.price AS 'Price',
    m.Quantity AS 'Quantity'
from medicine as m
where
    exists (
        -- to get only those having all three categories
        select 1
        from medicinecat as mc
        where mc.CatId in (1,2,3) and mc.MedID = m.MedID 
        having count(*) = 3
    )

如果你可以做一些通用的解决方案，比如

select
    m.MedID AS 'MedId',
    m.Name AS 'Name',
    m.price AS 'Price',
    m.Quantity AS 'Quantity'
from medicine as m
where
    not exists (
        select *
        from (values (1), (2), (3)) as tt(CatId)
            left outer join medicinecat as mc on mc.CatId = tt.CatId and mc.MedID = m.MedID
        where mc.CatId is null
    )

或

select
    m.MedID AS 'MedId',
    m.Name AS 'Name',
    m.price AS 'Price',
    m.Quantity AS 'Quantity'
from medicine as m
where
    exists (
        -- to get only those having all categories
        select 1
        from (values (1), (2), (3)) as tt(CatId)
            left outer join medicinecat as mc on mc.CatId = tt.CatId and mc.MedID = m.MedID
        having count(tt.CatId) = count(mc.CatId)
    )

Answer 2

一些选项（未经测试）

类别数量 DECLARE @categoryCount int SET @categoryCount =（SELECT COUNT（*）FROM Category WHERE catid IN（1,2,3））

SELECT medicine.MedID AS 'MedId', medicine.Name AS 'Name', medicine.price AS 'Price', medicine.Quantity AS 'Quantity'
FROM Medicine
WHERE @categoryCount = (SELECT COUNT(*) FROM MedicineCat WHERE MedicineCat.MedId = Medicine.MedId)

分组+有

SELECT medicine.MedID AS 'MedId', medicine.Name AS 'Name', medicine.price AS 'Price', medicine.Quantity AS 'Quantity'
FROM Medicine
    JOIN MedicineCat ON Medicine.MedId = MedicineCat.MedId
GROUP BY medicine.MedID, medicine.Name, medicine.price, medicine.Quantity
HAVING COUNT(*) = @categoryCount

多重存在

SELECT medicine.MedID AS 'MedId', medicine.Name AS 'Name', medicine.price AS 'Price', medicine.Quantity AS 'Quantity'
FROM Medicine
WHERE EXISTS (SELECT 1 FROM MedicineCat WHERE MedicineCat.MedId = 1)
    AND EXISTS (SELECT 1 FROM MedicineCat WHERE MedicineCat.MedId = 2)
    AND EXISTS (SELECT 1 FROM MedicineCat WHERE MedicineCat.MedId = 3)

查找具有多个链接行的行

2 个答案: