连接3个表并从所有表中检索所有记录 [英] Joining 3 tables and retrieve all the records from all the tables

问题描述

我正在联接三个表(执行完全外部联接)，以便可以从所有表中检索所有记录.我面临的问题是联接表的顺序.

I am joining three tables (performing a full outer join) so that I can retrieve all the records from all the tables. Problem that I am facing is with the order in which I join tables.

表格信息

替代文字http://img235.imageshack.us/img235/7980/tableinfoow1 .png

(1)如果我以TABLE1，TABLE2，TABLE3顺序连接表，我将获得两行记录，以记录团队B和级别1.

(1) If I join tables in TABLE1, TABLE2, TABLE3 sequence I get two rows for record with team B and Level 1.

SELECT DISTINCT 
    (CASE WHEN T0.[TEAM] IS NOT NULL THEN T0.[TEAM] WHEN T1.[TEAM] IS NOT NULL THEN T1.[TEAM] WHEN T2.[TEAM] IS NOT NULL THEN T2.[TEAM] ELSE T0.[TEAM] END) AS [TEAM], 
    (CASE WHEN T0.[LEVEL] IS NOT NULL THEN T0.[LEVEL] WHEN T1.[LEVEL] IS NOT NULL THEN T1.[LEVEL] WHEN T2.[LEVEL] IS NOT NULL THEN T2.[LEVEL] ELSE T0.[LEVEL] END) AS [LEVEL], 
    T0.[VALUE1] AS [VALUE1], 
    T1.[VALUE2] AS [VALUE2], 
    T2.[VALUE3] AS [VALUE3] 

FROM TABLE1 T0
FULL JOIN TABLE2 T1 ON T0.[TEAM] = T1.[TEAM] AND T0.[LEVEL] = T1.[LEVEL] 
FULL JOIN TABLE3 T2 ON T0.[TEAM] = T2.[TEAM] AND T0.[LEVEL] = T2.[LEVEL]

(2)如果我以TABLE2，TABLE3，TABLE1顺序连接表，则输出中的行数正确.

(2) If I join tables in TABLE2, TABLE3, TABLE1 sequence I get correct number of rows in the output.

SELECT DISTINCT 
    (CASE WHEN T0.[TEAM] IS NOT NULL THEN T0.[TEAM] WHEN T1.[TEAM] IS NOT NULL THEN T1.[TEAM] WHEN T2.[TEAM] IS NOT NULL THEN T2.[TEAM] ELSE T0.[TEAM] END) AS [TEAM], 
    (CASE WHEN T0.[LEVEL] IS NOT NULL THEN T0.[LEVEL] WHEN T1.[LEVEL] IS NOT NULL THEN T1.[LEVEL] WHEN T2.[LEVEL] IS NOT NULL THEN T2.[LEVEL] ELSE T0.[LEVEL] END) AS [LEVEL], 
    T0.[VALUE1] AS [VALUE1], 
    T1.[VALUE2] AS [VALUE2], 
    T2.[VALUE3] AS [VALUE3] 

FROM TABLE2 T0
FULL JOIN TABLE3 T1 ON T0.[TEAM] = T1.[TEAM] AND T0.[LEVEL] = T1.[LEVEL] 
FULL JOIN TABLE1 T2 ON T0.[TEAM] = T2.[TEAM] AND T0.[LEVEL] = T2.[LEVEL]

我面临的问题是我不知道输入表，并在运行时将所有这些表作为用户的输入并执行联接.我不能一次合并两个表，因为我的表一次可以合并三个以上的表(最多9个或10个).

Problem I am facing is that I am not aware of the input tables and take all these tables as an input from user at runtime and perform a join. I cannot merge two tables at a time since my table can technically merge more than three tables at a time (upto 9 or 10).

如何确保我从所有表中获取所有记录(使用完全外部联接)，但不能像#1中那样获得两行.

How can I ensure that I get all records from all tables (using full outer join) but DO not get two rows as in #1.

推荐答案

如果这是您需要的:

TEAM LEVEL  Value1  Value2  Value3
A   1        1       NULL    NULL
B   1        NULL    1000    900

然后您可以通过以下方法实现这一目标:

Then you can achieve that with the following:

SELECT [TEAM], [LEVEL], MAX(v1) Value1, MAX(v2) Value2, MAX(v3) Value3
FROM (
    SELECT [TEAM], [LEVEL], Value1 v1, NULL v2, NULL v3
    FROM TABLE1
    UNION
    SELECT [TEAM], [LEVEL], NULL, Value2, NULL
    FROM TABLE2
    UNION
    SELECT [TEAM], [LEVEL], NULL, NULL, Value3
    FROM TABLE3
) t0
GROUP BY [TEAM], [LEVEL]

，您可以根据需要使用任意数量的表.

and you can use as many tables as you need.

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