FULL OUTER JOIN的值出现在2个不同的字段中

Question

here is my query:

SELECT
COALESCE ([dbo].[RSA_BIRMINGHAM_1941$].TOS,
[dbo].[RSA_CARDIFFREGUS_2911$].TOS,[dbo].[RSA_CASTLEMEAD_1941$].TOS,
[dbo].[RSA_CHELMSFORD_1941$].TOS) AS [TOS Value]

,RSA_BIRMINGHAM_1941$.Percentage            AS [Birmingham]
,RSA_CARDIFFREGUS_2911$.Percentage          AS [Cardiff Regus]
,[dbo].[RSA_CASTLEMEAD_1941$].Percentage    AS [Castlemead]
,[dbo].[RSA_CHELMSFORD_1941$].Percentage    AS [Chelmsford]

FROM [dbo].[RSA_BIRMINGHAM_1941$] 
FULL OUTER JOIN [dbo].[RSA_CARDIFFREGUS_2911$] 
ON [dbo].[RSA_BIRMINGHAM_1941$].TOS = [dbo].[RSA_CARDIFFREGUS_2911$].TOS

FULL OUTER JOIN [dbo].[RSA_CASTLEMEAD_1941$] 
ON [dbo].[RSA_BIRMINGHAM_1941$].TOS = [dbo].[RSA_CASTLEMEAD_1941$].TOS

FULL OUTER JOIN [dbo].[RSA_CHELMSFORD_1941$] 
ON [dbo].[RSA_BIRMINGHAM_1941$].TOS = [dbo].[RSA_CHELMSFORD_1941$].TOS

And here is the output:

TOS Value        Birmingham   Cardiff Regus   Castlemead    Chelmsford
default (DSCP 0)   61.37%       61.74%         99.48%         79.78%
af11 (DSCP 10)     15.22%       4.63%          0.00%          6.16%
af33 (DSCP 30)     11.49%       15.44%         NULL           7.33%
af31 (DSCP 26)     8.86%        13.85%         0.01%          5.59%
ef (DSCP 46)       1.91%        3.72%          0.49%          0.91%
af41 (DSCP 34)     0.70%        0.03%          0.01%          0.05%
cs4 (DSCP 32)      0.15%        0.20%          NULL           0.10%
af12 (DSCP 12)     0.12%        NULL           NULL           NULL
cs3 (DSCP 24)      0.06%        0.11%          0.01%          0.04%
af21 (DSCP 18)     0.05%        0.05%          0.00%          0.02%
cs6 (DSCP 48)      NULL         0.23%          NULL           NULL
cs6 (DSCP 48)      NULL         NULL           0.00%          NULL
af32 (DSCP 28)     NULL         NULL           NULL           0.02%

If you have a look at the TOS column and look at value cs6 (DSCP 48) you will see that it has been duplicated. there should be only 1 cs6 (DSCP 48) row but for some reason the Castlemead value (0.00%) for cs6 (DSCP 48) has been created as a separate column.

there should be only one row per TOS value if that makes sense so please tell where did I go wrong?

Answer 1

The results you get are as expected. This is because the joins are all relative to the first table. If there is a TOS in the second table that has no match with the first table that will generate a new record. If there is a TOS in the third table that has no match with the first table that will again generate a new record. There is no clue for the engine to know that such instances should be combined into one result.

There are probably several ways to resolve this. I will suggest one where you introduce a UNION sub select that will combine all TOS values, and then an INNER JOIN to each of the four tables.

SELECT       REF.TOS AS [TOS Value]
            ,RSA_BIRMINGHAM_1941$.Percentage    AS [Birmingham]
            ,RSA_CARDIFFREGUS_2911$.Percentage  AS [Cardiff Regus]
            ,RSA_CASTLEMEAD_1941$.Percentage    AS [Castlemead]
            ,RSA_CHELMSFORD_1941$.Percentage    AS [Chelmsford]

FROM       ( SELECT TOS FROM RSA_BIRMINGHAM_1941$   UNION
             SELECT TOS FROM RSA_CARDIFFREGUS_2911$ UNION
             SELECT TOS FROM RSA_CASTLEMEAD_1941$   UNION
             SELECT TOS FROM RSA_CHELMSFORD_1941$
           ) AS REF
INNER JOIN RSA_BIRMINGHAM_1941$   ON REF.TOS = RSA_BIRMINGHAM_1941$.TOS
INNER JOIN RSA_CARDIFFREGUS_2911$ ON REF.TOS = RSA_CARDIFFREGUS_2911$.TOS
INNER JOIN RSA_CASTLEMEAD_1941$   ON REF.TOS = RSA_CASTLEMEAD_1941$.TOS
INNER JOIN RSA_CHELMSFORD_1941$   ON REF.TOS = RSA_CHELMSFORD_1941$.TOS

Answer 2

Queries are so much easier to write and to read with table aliases. The problem is the matching in the second FULL OUTER JOIN . The FROM clause needs to look like this:

FROM [dbo].[RSA_BIRMINGHAM_1941$] b FULL OUTER JOIN
     [dbo].[RSA_CARDIFFREGUS_2911$] cr
     ON b.TOS = cr.TOS FULL OUTER JOIN
     [dbo].[RSA_CASTLEMEAD_1941$] cm
     ON cm.TOS IN (b.TOS, cr.TOS) FULL OUTER JOIN
     [dbo].[RSA_CHELMSFORD_1941$] cf
     ON cf.TOS IN (b.TOS, cr.TOS, cm.TOS)

In other words, by comparing to only one TOS field in the later joins, you might be joining to an unmatched column -- and hence getting a duplicate. One FULL OUTER JOIN is fine. Multiple FULL OUTER JOIN s are tricky. I often use UNION ALL queries instead.

Answer 3

Thanks to @trincot as he is the one who layed the fondation to the outcome that i was looking for. here is the query that has solved my issue:

SELECT       REF.TOS AS [TOS Value]
        ,RSA_BIRMINGHAM_1941$.Percentage    AS [Birmingham]
        ,RSA_CARDIFFREGUS_2911$.Percentage  AS [Cardiff Regus]
        ,RSA_CASTLEMEAD_1941$.Percentage    AS [Castlemead]
        ,RSA_CHELMSFORD_1941$.Percentage    AS [Chelmsford]

 FROM    
         (SELECT TOS FROM RSA_BIRMINGHAM_1941$   UNION
         SELECT TOS FROM RSA_CARDIFFREGUS_2911$ UNION
         SELECT TOS FROM RSA_CASTLEMEAD_1941$   UNION
         SELECT TOS FROM RSA_CHELMSFORD_1941$) AS REF

       FULL OUTER JOIN RSA_BIRMINGHAM_1941$   ON REF.TOS =  
       RSA_BIRMINGHAM_1941$.TOS
       FULL OUTER JOIN RSA_CARDIFFREGUS_2911$ ON REF.TOS =
       RSA_CARDIFFREGUS_2911$.TOS
       FULL OUTER JOIN RSA_CASTLEMEAD_1941$   ON REF.TOS = 
       RSA_CASTLEMEAD_1941$.TOS
       FULL OUTER JOIN RSA_CHELMSFORD_1941$   ON REF.TOS = 
       RSA_CHELMSFORD_1941$.TOS

       ORDER BY [TOS Value]

and the result is the following as expected:

TOS Value      Birmingham   CardiffRegus    Castlemead  Chelmsford
af11 (DSCP 10)  15.22%      4.63%           0.00%        6.16%
af12 (DSCP 12)  0.12%       NULL            NULL         NULL
af21 (DSCP 18)  0.05%       0.05%           0.00%        0.02%
af31 (DSCP 26)  8.86%       13.85%          0.01%        5.59%
af32 (DSCP 28)  NULL        NULL            NULL         0.02%
af33 (DSCP 30)  11.49%      15.44%          NULL         7.33%
af41 (DSCP 34)  0.70%       0.03%           0.01%        0.05%
cs3 (DSCP 24)   0.06%       0.11%           0.01%        0.04%
cs4 (DSCP 32)   0.15%       0.20%           NULL         0.10%
cs6 (DSCP 48)   NULL        0.23%           0.00%        NULL
defau(DSCP 0)   61.37%      61.74%          99.48%       79.78%
ef (DSCP 46)    1.91%       3.72%           0.49%        0.91%