Question

我正在对Stack Overflow转储进行分析。

问题陈述：我有4个表，并且要求给出格式的结果。

Table 1: UserID Year QuestionsOnTopicA
Table 2: UserID Year AnswersOnTopicA
Table 3: UserID Year QuestionsOnTopicB
Table 4: UserID Year AnswersOnTopicB

期望的输出：

UserID Year QuestionsOnTopicA AnswersOnTopicA QuestionsOnTopicB AnswersOnTopicB

UserID列应包含来自所有4个表的条目。

我尝试在表上执行内部和外部联接，但结果不正确。内连接（仅返回第一个表1中存在的用户ID）外连接（仅为表1中的userid返回其他列）

不确定联合在这种情况下是否有意义。

正在data.stackexchange.com/stackoverflow

上执行查询

实施例

表1：1001,2010,5 || 1001,2011,3 || 1002,2010,4，

表2：1001,2010,10 || 1001,2011,7 || 1002,2010,5

表3：1002,2010,5

表4：1001,2010,10 || 1004,2011,5

输出：

1001,2010,5,10,0,10

1001,2011,3,7,0,0

1002,2010,4,5,5,0

1004,2011,0,0,0,5

Answer 1

使用这个SQL可能是？

SELECT a.UserID, a.Year,
       a.QuestionsOnTopicA,
       b.AnswersOnTopicA,
       c.QuestionsOnTopicB,
       d.AnswersOnTopicB
FROM Table 1 a,
     Table 2 b,
     Table 3 c,
     Table 4 d
WHERE a.UserID = b.UserID
  AND b.UserID = c.UserID
  AND c.UserID = d.UserID
  AND d.UserID = a.UserID

Answer 2

select coalesce(a.UserID, b.UserID, c.UserID, d.UserID),
       coalesce(a.Year, b.Year, c.Year, d.Year),
       a.QuestionsOnTopicA, b.AnswersOnTopicA,
       c.QuestionsOnTopicB, d.AnswersOnTopicB
from Table1 a full outer join Table2 b on a.UserID = b.UserID and a.Year = b.Year
              full outer join Table3 c on (c.UserID = b.UserID or c.UserID = a.UserID) 
                                          and (c.Year = b.Year or c.Year = a.Year)
              full outer join Table4 d on (d.UserID = c.UserID or d.UserID = b.UserID or d.UserID = a.UserID) 
                                          and (d.Year = a.Year or d.Year = b.Year or d.Year = a.Year);

Answer 3

好的，这可以按预期工作：

SELECT  COALESCE(A.UserID,B.UserID,C.UserID,D.UserID) UserID,
        COALESCE(A.[Year],B.[Year],C.[Year],D.[Year]) [Year],
        ISNULL(A.QuestionsOnTopicA,0) QuestionsOnTopicA,
        ISNULL(B.AnswersOnTopicA,0) AnswersOnTopicA,
        ISNULL(C.QuestionsOnTopicB,0) QuestionsOnTopicB,
        ISNULL(D.AnswersOnTopicB,0) AnswersOnTopicB
FROM Table1 A
FULL JOIN Table2 B
    ON A.UserID = B.UserID
    AND A.[Year] = B.[Year]
FULL JOIN Table3 C
    ON COALESCE(A.UserID,B.UserID) = C.UserID
    AND COALESCE(A.[Year],B.[Year]) = C.[Year]
FULL JOIN Table4 D
    ON COALESCE(A.UserID,B.UserID,C.UserID) = D.UserID
    AND COALESCE(A.[Year],B.[Year],C.[Year]) = D.[Year]

Here is a sqlfiddle及其演示。

结果是：

╔════════╦══════╦═══════════════════╦═════════════════╦═══════════════════╦═════════════════╗
║ UserID ║ Year ║ QuestionsOnTopicA ║ AnswersOnTopicA ║ QuestionsOnTopicB ║ AnswersOnTopicB ║
╠════════╬══════╬═══════════════════╬═════════════════╬═══════════════════╬═════════════════╣
║   1001 ║ 2010 ║                 5 ║              10 ║                 0 ║              10 ║
║   1001 ║ 2011 ║                 3 ║               7 ║                 0 ║               0 ║
║   1002 ║ 2010 ║                 4 ║               5 ║                 5 ║               0 ║
║   1004 ║ 2011 ║                 0 ║               0 ║                 0 ║               5 ║
╚════════╩══════╩═══════════════════╩═════════════════╩═══════════════════╩═════════════════╝

Answer 4

首先，您应该使用内部联接从表中检索数据。然后，您应该使用SQL Server Pivot，如此link。

所示

返回多个表的结果

4 个答案: