Using Item Sales Table from Example Database, let us calculate and show the total Quantity we sold of each Product.
This can be easily done with a group by, but lets assume we to 'rotate' our result table in a way that for each Product Id we have a column.
SELECT [100], [145]
  FROM (SELECT ItemId , Quantity
          FROM #ItemSalesTable
       ) AS pivotIntermediate
 PIVOT (   SUM(Quantity)
           FOR ItemId IN ([100], [145])
       ) AS pivotTable
Since our 'new' columns are numbers (in the source table), we need to square brackets []
This will give us an output like
| 100 | 145 | 
|---|---|
| 45 | 18 |