Multiple FULL OUTER JOIN on multiple tables

Question

I have multiple outer joins

SELECT  A.column2
        , B.column2
        , C.column2
FROM 
(
    (SELECT month, column2 FROM table1) A
    FULL OUTER JOIN
          


        

Answer 1

Use option with COALESCE function to determine a column grouping.

SELECT COALESCE(t1.Month, t2.Month, t3.Month) AS Month, 
       SUM(ISNULL(t1.Col1, 0)) AS t1Col1, 
       SUM(ISNULL(t2.Col1, 0)) AS t2Col1, 
       SUM(ISNULL(t3.Col1, 0)) AS t3Col1
FROM dbo.table1 t1 FULL OUTER JOIN dbo.table2 t2 ON t1.Month = t2.Month
                   FULL OUTER JOIN dbo.table3 t3 ON t1.Month = t3.Month
GROUP BY COALESCE(t1.Month, t2.Month, t3.Month)