问题
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.
Table Information
alt text http://img235.imageshack.us/img235/7980/tableinfoow1.png
(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) 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]
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).
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.
回答1:
If this is what you need:
TEAM LEVEL Value1 Value2 Value3
A 1 1 NULL NULL
B 1 NULL 1000 900
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]
and you can use as many tables as you need.
回答2:
That's the definition of a FULL OUTER JOIN (which, when used, is almost invariably an indication of a poor design - I use a FULL OUTER JOIN about once a year).
Perhaps if you gave the results you were looking for?
I'm thinking UNION, GROUP BY and COALESCE.
回答3:
What you need is to add an additional match condition on the second join expression to allow it to match the second table's team/level values. I've also simplified the team/level column expressions using ISNULL:
SELECT DISTINCT
ISNULL(T0.[TEAM],ISNULL(T1.[TEAM],T2.[TEAM])) AS [TEAM],
ISNULL(T0.[LEVEL],ISNULL(T1.[LEVEL],T2.[LEVEL])) AS [LEVEL],
T0.[VALUE1], T1.[VALUE2], T2.[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])
OR (T1.[TEAM] = T2.[TEAM] AND T1.[LEVEL] = T2.[LEVEL])
See? T1 didn't show on the same row as T2 because you never allowed that as a match possibility.
回答4:
AS u define in yru query distinct that means there r multiple entry along one in this union all is the best to use because there are duplication in the data.
SELECT [TEAM], [LEVEL], MAX(v1) Value1, MAX(v2) Value2, MAX(v3) Value3
FROM (
SELECT [TEAM], [LEVEL], v1, NULL v2, NULL v3
FROM TABLE1
UNION ALL
SELECT [TEAM], [LEVEL], NULL v1, V2, NULL v3
FROM TABLE2
UNION ALL
SELECT [TEAM], [LEVEL], NULL V1, NULL V2, V3
FROM TABLE3
) t0
GROUP BY [TEAM], [LEVEL]
来源：https://stackoverflow.com/questions/441939/joining-3-tables-and-retrieve-all-the-records-from-all-the-tables