Read-only trigger

(Example in Oracle)

         CREATE OR REPLACE TRIGGER AGENCY_PF.EXAMPLE_TRIGGER
            INSTEAD OF INSERT OR UPDATE OR DELETE ON AGENCY_PF.YOUR_TABLE
            FOR EACH ROW
               BEGIN
               IF INSERTING THEN
                  NULL;
               ELSIF UPDATING THEN
                  NULL;
               ELSE
                  NULL;
               END IF;
            END;

(Example in SQL Server)

         CREATE TRIGGER AGENCY_PF.EXAMPLE_TRIGGER ON AGENCY_PF.YOUR_TABLE 
         INSTEAD OF INSERT, UPDATE, DELETE
         AS
         BEGIN
            IF EXISTS(SELECT * FROM DELETED)
            BEGIN         
               IF EXISTS(SELECT * FROM INSERTED) 
               BEGIN
               --Update being performed, insert appropriate code here.
               END
            ELSE 
            BEGIN
            --Delete being performed, insert appropriate code here.
            END 
         END     
         ELSE
            BEGIN 
               IF EXISTS(SELECT * FROM INSERTED) 
               BEGIN
               --Insert being performed, insert appropriate code here.
               END 
            END
         END