Question

I have a single database table that stores week entries.

Id        Value     WeekId
1         1.0000    1
2         2.0000    1

There can be up to three entries with the same week.

So I figured using a self join would solve this

SELECT w1.Value, w2.Value, w3.Value 
FROM [List].[dbo].[testWeekEntries] as w1 
LEFT OUTER JOIN [List].[dbo].[testWeekEntries] as w2 ON w1.WeekId = w2.weekId 
LEFT OUTER JOIN [List].[dbo].[testWeekEntries] as w3 ON w2.WeekId = w3.WeekId 
WHERE w1.Id < w2.Id AND w2.Id < w3.Id

The problem: It worls fine with the maximum number of entries however it doesn’t pull back a row with one or two entries.

Is there a different type of join I can use to pull back a row with only one or two entries or a different way of approaching this?

Answer 1

These entries are not returning because your WHERE clause explicitly filters them out when the joined tables return NULL values.

This solution adds a sequential rownumber to each record, restarting to 1 for each week. This allows you to use this sequential number in a PIVOT statement

SQL 2000 Statement

SELECT  *
FROM    (
          SELECT  (SELECT  COUNT(*) 
                   FROM    testWeekEntries 
                   WHERE   Id <= we.Id 
                           AND WeekId = we.WeekId) as rn
                  , Value
                  , WeekId
          FROM    testWeekEntries we
        ) q
PIVOT   (MAX(Value) FOR rn IN ([1],[2],[3]) ) AS PVT

SQL 2008 Statement

;WITH q AS (
SELECT  rn = ROW_NUMBER() OVER (PARTITION BY WeekId ORDER BY Id)
        , Id
        , Value
        , WeekId
FROM    [testWeekEntries] as w1 
)
SELECT  Value
        , (SELECT Value FROM q q1 WHERE q1.rn = q.rn + 1 AND q1.WeekId = q.WeekId)
        , (SELECT Value FROM q q2 WHERE q2.rn = q.rn + 2 AND q2.WeekId = q.WeekId)
FROM    q
WHERE   q.rn = 1