連接來自兩個結果集的列

Question

我有一個桌子group

CREATE TABLE
GROUP (id , HOST , participant)

INSERT INTO GROUP(id, HOST, participant)
VALUES (1, 1000, 2000)

INSERT INTO GROUP (id, HOST, participant)
VALUES (1, 1000, 2000)

customer表

insert into customer( custmerid, customername, alias) values (1000,'abccorp', 'abc')
insert into customer( custmerid, customername, alias) values (2000,'bcacorp', 'bca')
insert into customer( custmerid, customername, alias) values (3000,'lcacorp', 'lca')

現在我想寫一個視圖

groupID, host participation
1 abccorp bcacorp
2 abccorp null
3 null lcacorp

我怎么能得到這個？ 我看到該組織需要兩個加入。 但是我怎么能得到它呢？

謝謝。

Answer 1

如果我沒有誤解您的問題，以下聲明將返回您所需的結果。

我正在使用以下假設

• Host已映射到custmerid
• Participant已映射到custmerid
• 您提供的輸入數據不完整

請注意，如果custmerid不是您的問題中的拼寫錯誤，我建議您將其完全拼寫為customerid

SQL語句

SELECT  groupid = g.id
        , host = chost.customername
        , participation = cparticipant.customername     
FROM    [Group] g
        LEFT OUTER JOIN Customer chost ON chost.custmerid = g.Host
        LEFT OUTER JOIN Customer cparticipant ON cparticipant.custmerid = g.Participant

測試數據

;WITH [Group](ID, Host, Participant) AS (
    SELECT 1, 1000, 2000
    UNION ALL SELECT 2, 1000, NULL
    UNION ALL SELECT 3, NULL, 3000
)
, Customer (custmerid, customername, alias) AS (
    SELECT 1000, 'abccorp', 'abc'
    UNION ALL SELECT 2000, 'bcacorp', 'bca'
    UNION ALL SELECT 3000, 'lcacorp', 'lca'
)
SELECT  groupid = g.id
        , host = chost.customername
        , participation = cparticipant.customername     
FROM    [Group] g
        LEFT OUTER JOIN Customer chost ON chost.custmerid = g.Host
        LEFT OUTER JOIN Customer cparticipant ON cparticipant.custmerid = g.Participant

輸出量

groupid     host    participation
----------- ------- -------------
1           abccorp bcacorp
2           abccorp NULL
3           NULL    lcacorp