Add trigger callbacks

sql/core.go

@@ -820,6 +820,7 @@ type TriggerDefinition struct {
 	Name            string    // The name of this trigger. Trigger names in a database are unique.
 	CreateStatement string    // The text of the statement to create this trigger.
 	CreatedAt       time.Time // The time that the trigger was created.
+	Callback        func()    // Optional Go callback invoked after each row the trigger fires on. Not persisted.
 }
 
 // TriggerDatabase is a Database that supports the creation and execution of triggers. The engine handles all parsing

sql/plan/trigger.go

@@ -172,9 +172,15 @@ func (t *triggerIter) Next(ctx *sql.Context) (row sql.Row, returnErr error) {
 	// For some logic statements, we want to return the result of the logic operation as our row, e.g. a Set that alters
 	// the fields of the new row
 	if ok, returnRow := shouldUseLogicResult(logic, logicRow); ok {
+		if t.TriggerDefinition.Callback != nil {
+			t.TriggerDefinition.Callback()
+		}
 		return returnRow, nil
 	}
 
+	if t.TriggerDefinition.Callback != nil {
+		t.TriggerDefinition.Callback()
+	}
 	return childRow, nil
 }