Question

I am creating a temp table from a query that generates data from SQL functions. I would like to use this temp table to perform an insert for each row of data from the temp table. What is the best way to proceed with this?

#tmpTable is as follows (not all columns shown for simplicity):

EmpID       WorkHours      HourlyEquivalent     WeekOf
asmith      12             8.94                 12/5/2011
bjones      23.5           12.75                12/5/2011
criley      40             7.89                 12/5/2011

The table EmpHours will already be filled in with the employees hours but needs to be updated with their hourly equivalent (calculated from the aforementioned functions). I want to perform an UPDATE for each employee from the temp table as follows:

UPDATE EmpHours
SET HourlyEquivalent
WHERE WeekOf = #tmpTable.WeekOf
    AND EmpID = #tmpTable.EmpID

The number of UPDATEs I would need to perform is under 50 if that matters.

Answer 1

SQL is much more efficient at doing operations like this in a single command, instead of a row-by-row update. Even though you don’t have very many rows in this scenario, it’s still a good habit to take a set based approach instead of using a loop or a cursor.

UPDATE e
SET HourlyEquivalent = t.HourlyEquivalent
FROM
    EmpHours e JOIN
    #tmpTable t ON t.WeekOf = e.WeekOf AND t.EmpID = e.EmpID