Multirow Considerations

Multirow considerations are particularly important when the function of a trigger is to recalculate summary values, or provide ongoing tallies.

Triggers used to maintain summary values should contain group by clauses or subqueries that perform implicit grouping. This creates summary values when more than one row is being inserted, updated, or deleted. Since a group by clause imposes extra overhead, the following examples are written to test whether @@rowcount = 1, meaning that only one row in the trigger table was affected. If @@rowcount = 1, the trigger actions take effect without a group by clause.

• Insert Trigger Example Using Multiple Rows
  Use a insert trigger to update a column everytime a row is added.
• Delete Trigger Example Using Multiple Rows
  Use a delete trigger to update a column when rows are deleted.
• Update Trigger Example Using Multiple Rows
  Use a trigger to update a column everytime a field in a row is updated.
• Conditional Insert Trigger Example Using Multiple Rows
  You do not have to roll back all data modifications simply because some of them are unacceptable. Using a correlated subquery in a trigger can force the trigger to examine the modified rows one by one.