Understanding PIVOT function in T-SQL

Question

I am very new to SQL.

I have a table like this:

ID | TeamID | UserID | ElementID | PhaseID | Effort
-------------------------------------------------         


        

Answer 1

A pivot is used to convert one of the columns in your data set from rows into columns (this is typically referred to as the spreading column). In the example you have given, this means converting the PhaseID rows into a set of columns, where there is one column for each distinct value that PhaseID can contain - 1, 5 and 6 in this case.

These pivoted values are grouped via the ElementID column in the example that you have given.

Typically you also then need to provide some form of aggregation that gives you the values referenced by the intersection of the spreading value (PhaseID) and the grouping value (ElementID). Although in the example given the aggregation that will be used is unclear, but involves the Effort column.

Once this pivoting is done, the grouping and spreading columns are used to find an aggregation value. Or in your case, ElementID and PhaseIDX lookup Effort.

Using the grouping, spreading, aggregation terminology you will typically see example syntax for a pivot as:

WITH PivotData AS
(
    SELECT 
        , 
        , 
    FROM 
)
SELECT , 
FROM PivotData
    PIVOT (()
        FOR  IN ));

This gives a graphical explanation of how the grouping, spreading and aggregation columns convert from the source to pivoted tables if that helps further.