Combining two T-SQL pivot queries in one - sql

Question

Suppose you had this table:
CREATE TABLE Records
(
RecordId int IDENTITY(1,1) NOT NULL,
CreateDate datetime NOT NULL,
IsSpecial bit NOT NULL
CONSTRAINT PK_Records PRIMARY KEY(RecordId)
)
Now a report needs to be created where the total records and the total special records are broken down by month. I can use these two queries separately:
-- TOTAL RECORDS PER MONTH
SELECT January, February, March, April, May, June,
July, August, September, October, November, December
FROM (
SELECT RecordId, DATENAME(MONTH, CreateDate) AS RecordMonth
FROM dbo.Records
) AS SourceTable
PIVOT (
COUNT(RecordId) FOR RecordMonth IN (January, February, March, April, May, June,
July, August, September, October, November, December)
) AS PivotTable;
-- TOTAL SPECIAL RECORDS PER MONTH
SELECT January, February, March, April, May, June,
July, August, September, October, November, December
FROM (
SELECT RecordId, DATENAME(MONTH, CreateDate) AS RecordMonth
FROM dbo.Records
WHERE IsSpecial = 1
) AS SourceTable
PIVOT (
COUNT(RecordId) FOR RecordMonth IN (January, February, March, April, May, June,
July, August, September, October, November, December)
) AS PivotTable;
The results might look like this:
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
total 0 0 2 2 1 0 0 1 2 1 2 4
total special 0 0 1 0 1 0 0 0 0 0 0 2
Is it possible to combine these two queries into a single more efficient query?

Answer 1

I would do it like this:
SELECT
CASE SQ.total_type
WHEN 1 THEN 'total special'
WHEN 2 THEN 'total expensive'
ELSE 'total'
END AS total_type,
SUM(CASE WHEN MONTH(R.CreateDate) = 1 THEN 1 ELSE 0 END) AS January,
SUM(CASE WHEN MONTH(R.CreateDate) = 2 THEN 1 ELSE 0 END) AS February,
SUM(CASE WHEN MONTH(R.CreateDate) = 3 THEN 1 ELSE 0 END) AS March,
...
FROM
dbo.Records R
INNER JOIN
(
SELECT 0 AS total_type UNION ALL -- All
SELECT 1 UNION ALL -- IsSpecial
SELECT 2 -- IsExpensive
) AS SQ ON
(R.IsSpecial | (R.IsExpensive * 2)) & SQ.total_type = SQ.total_type
GROUP BY
SQ.total_type
ORDER BY
SQ.total_type DESC

Answer 2

You can only have one aggregate (COUNT(RecordId)) per pivot so all you do is combine into one result set with a UNION ALL with a suitable extra column to identify each pivot.
Otherwise, you have no way to distinguish the 2 different aggregates in the pivot

Answer 3

Thanks for the solution Tom, that answers my pivot question.
Too bad for me I had the wrong question. For my problem I'm now feeling it would be better to use a plain grouping query like this instead:
SELECT DATENAME(MONTH, CreateDate) AS Month,
COUNT(*) AS Total,
SUM(CASE
WHEN IsSpecial = 1 THEN 1
ELSE 0
END) AS TotalSpecial,
SUM(CASE
WHEN IsExpensive = 1 THEN 1
ELSE 0
END) AS TotalExpensive
FROM Records
GROUP BY DATENAME(MONTH, CreateDate);
Then all that is left to do is rotate the results before they are presented. Nice to know eh?