Question

我遇到一个问题，需要执行多个查询才能找到结果。如何在一个查询中完成此操作，因为我需要提高性能？

基本上，我需要从表A中选择与给定用户的项目共享表B中的常用行的项目。

从Usertable
中选择人员

如果

1）他们拥有用户已经拥有的任何成果

示例：

罗杰有苹果和橘子。肯尼斯有芒果和苹果。朱莉有芒果。

问题：选择与Roger分享共同成果的人

The Query挑选Kenneth，因为他与Roger共享一个项目（苹果）。

显然，我可以使用3个查询并按照以下步骤完成此操作：

1）选择人员

2）运行每个用户项目的foreach

3）如果用户包含Roger的水果，请选择它们

如何在一个查询中执行此操作？

Answer 1

没有精确的表结构无法给出正确的答案。但您可以使用'IN'子句

select * from Usertable a join userfruit b on .....
where b. fruit in ( select fruit from userfruit where username='Roger')

请检查此演示SQLFiidle

Answer 2

SELECT a.username 
FROM Usertable a 
JOIN userfruit b 
    ON a.user_id = b.user_id 
WHERE 
    a.fruit IN (
        SELECT b.fruit 
        FROM userfruit
        WHERE username='Roger'
    );

Answer 3

执行如下所示的选择，并在迭代结果时添加到结构Map<UserName, List<Fruits>>。

select usertable.name, userfruits.fruitname from usertable join userfruits on (usertable.name = userfruits.username) order by usertable.name;

这将为您提供以下类型的结果：

Name             |FruitName
----------------------------
Julie            |Mangoes
Kenneth          |Apple
Kenneth          |Mangoes
Roger            |Apple
Roger            |Orange

Answer 4

CREATE TABLE #tmpPerson (
    Id INT,
    Name NVARCHAR(32)
)

CREATE TABLE #tmpFruit (
    Id INT,
    Name NVARCHAR(32)
)

CREATE TABLE #tmpPersonFruit (
    PersonId INT,
    FruitId INT
)

INSERT INTO #tmpPerson (Id, Name) VALUES (1, 'Roger')
INSERT INTO #tmpPerson (Id, Name) VALUES (2, 'Kenneth')
INSERT INTO #tmpPerson (Id, Name) VALUES (3, 'Julie')

INSERT INTO #tmpFruit (Id, Name) VALUES (1, 'Apples')
INSERT INTO #tmpFruit (Id, Name) VALUES (2, 'Oranges')
INSERT INTO #tmpFruit (Id, Name) VALUES (3, 'Mangoes')

INSERT INTO #tmpPersonFruit (PersonId, FruitId) VALUES(1, 1)
INSERT INTO #tmpPersonFruit (PersonId, FruitId) VALUES(1, 2)
INSERT INTO #tmpPersonFruit (PersonId, FruitId) VALUES(2, 1)
INSERT INTO #tmpPersonFruit (PersonId, FruitId) VALUES(2, 3)
INSERT INTO #tmpPersonFruit (PersonId, FruitId) VALUES(3, 3)

GO

DECLARE @Person NVARCHAR(64)
SET @Person = 'Roger'

SELECT          Person.Name AS PersonName,
                Fruit.Name AS FruitName

FROM            #tmpPerson AS Person

INNER JOIN      #tmpPersonFruit AS PersonFruit
    ON          Person.Id = PersonFruit.PersonId

INNER JOIN( SELECT          F.*
                FROM (          SELECT          *
                                FROM            #tmpPerson
                                WHERE           Name = @Person) AS P
                INNER JOIN      #tmpPersonFruit AS PF
                    ON          P.Id = PF.PersonId

                INNER JOIN      #tmpFruit AS F
                    ON          PF.FruitId = F.Id) AS Fruit
    ON          PersonFruit.FruitId = Fruit.Id

GO

DROP TABLE #tmpPerson
DROP TABLE #tmpFruit
DROP TABLE #tmpPersonFruit

如果您需要完整解释其原因，请与我们联系。

编写SQL查询以简化给定的示例

4 个答案: