sql turn dynamic rows into columns - sql

Question

Subject: Issues and their tasks.
Environment: SQL Server 2008 or above
Database tables: Issues, Tasks, and IssuesTasks
Let's say I have a single input screen that deals with a single issue and their associated tasks.
We're dealing with Issue1 and there are 7 tasks listed to check off.
The user checks 3 of the 7 tasks as completed and saves to database.
Is it possible to write a SQL that shows Issue1 with the 7 tasks on the same row? (Keep in mind only 3 were checked, so the others should be null).
Also note, there are only 3 tasks in the IssuesTasks join table representing what the user checked.

Answer 1

Use SQL server build in PIVOT function:
SELECT <non-pivoted column>,
[first pivoted column] AS <column name>,
[second pivoted column] AS <column name>,
...
[last pivoted column] AS <column name>
FROM
(<SELECT query that produces the data>)
AS <alias for the source query>
PIVOT
(
<aggregation function>(<column being aggregated>)
FOR
[<column that contains the values that will become column headers>]
IN ( [first pivoted column], [second pivoted column],
... [last pivoted column])
) AS <alias for the pivot table>
<optional ORDER BY clause>;
You can use the PIVOT and UNPIVOT relational operators to change a table-valued expression into another table. PIVOT rotates a table-valued expression by turning the unique values from one column in the expression into multiple columns in the output, and performs aggregations where they are required on any remaining column values that are wanted in the final output. UNPIVOT performs the opposite operation to PIVOT by rotating columns of a table-valued expression into column values.
Simple AdventureWorks example:
-- Pivot table with one row and five columns
SELECT 'AverageCost' AS Cost_Sorted_By_Production_Days,
[0], [1], [2], [3], [4]
FROM
(SELECT DaysToManufacture, StandardCost
FROM Production.Product) AS SourceTable
PIVOT
(
AVG(StandardCost)
FOR DaysToManufacture IN ([0], [1], [2], [3], [4])
) AS PivotTable;
More complex example:
USE AdventureWorks2008R2;
GO
SELECT VendorID, [250] AS Emp1, [251] AS Emp2, [256] AS Emp3, [257] AS Emp4, [260] AS Emp5
FROM
(SELECT PurchaseOrderID, EmployeeID, VendorID
FROM Purchasing.PurchaseOrderHeader) p
PIVOT
(
COUNT (PurchaseOrderID)
FOR EmployeeID IN
( [250], [251], [256], [257], [260] )
) AS pvt
ORDER BY pvt.VendorID;
For more information see here

Answer 2

While you've not provided schema for your tables, it's not easy to write you exact query, but take a look at this
select
I.Id,
I.Name,
max(case when IT.TaskId = 1 then T.Name end) as Task1,
max(case when IT.TaskId = 2 then T.Name end) as Task2,
max(case when IT.TaskId = 3 then T.Name end) as Task3,
max(case when IT.TaskId = 4 then T.Name end) as Task4,
max(case when IT.TaskId = 5 then T.Name end) as Task5,
max(case when IT.TaskId = 6 then T.Name end) as Task6,
max(case when IT.TaskId = 7 then T.Name end) as Task7
from Issues as I
left outer join IssuesTasks as IT on IT.IssueId = I.Id
left outer join Tasks as T on T.Id = IT.TaskID
group by I.Id, I.Name;
See SQL FIDDLE example

Answer 3

Please excuse me if this isn't kosher; I'm still getting acclimated with the rules around here (long time reader of stackoverflow, first day posting). I actually just wrote an article on this on my new blog, and I sincerely think it would help. Basically, you can dynamically build your pivoted column values and pass them in to a dynamically-built PIVOT query like this:
IF (OBJECT_ID('tempdb..#TEMP') is not null) DROP TABLE #TEMP
DECLARE #cols NVARCHAR(2000)
SELECT DISTINCT DATE
INTO #TEMP
FROM T_EMPLOYEE_PRODUCTIVITY
SELECT #cols = ISNULL(#cols + ',', '') + '[' + CONVERT(NVARCHAR, DATE) + ']'
FROM #TEMP
ORDER BY DATE
SELECT #cols
DECLARE #query NVARCHAR(4000)
SET #query = 'SELECT EMPLOYEE_NAME, ' + #cols +
'FROM
(
SELECT EMPLOYEE_NAME, DATE, UNITS
FROM T_EMPLOYEE_PRODUCTIVITY
) AS SourceTable
PIVOT
(
SUM(UNITS)
FOR DATE IN ('+ #cols + ')
) AS PivotTable
ORDER BY EMPLOYEE_NAME'
SELECT #query
EXECUTE(#query)
If you need a more detailed explanation with sample data, check it out here: http://thrillhouseblog.blogspot.com/2013/08/dynamic-pivot-query-in-tsql-microsoft.html
I hope this helps!