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sal_diff); END; / keyword if you want the trigger to query or change the same table, because triggers can only do that after the initial changes are applied and the table is back in a consistent state.

Therefore, do not create triggers that depend on the order in which rows are processed.

For example, do not assign a value to a global package variable in a row trigger if the current value of the global variable is dependent on the row being processed by the row trigger.

That may not sound like too useful a thing now, but the MERGE statement represents a very powerful way to bring a database table into sync with an external source of data (such as a flat file feed from a remote system). The value for DEPTNO should be 50, DNAME should be “PROGRAMMING”, and LOC should be “BALTIMORE”.

This chapter turns the tables, and focuses on the following three topic areas: For ease in finding them when you need them, recipes in this chapter have been grouped by topic: all the insertion recipes come first, followed by the update recipes, and finally recipes for deleting data. It begins with the simple problem of inserting a single row.

For example, a table and a trigger can have the same name (however, to avoid confusion, this is not recommended). If a triggering statement includes a column list, the trigger is fired only when one of the specified columns is updated.

If a triggering statement omits a column list, the trigger is fired when any column of the associated table is updated.

Any view that contains one of those constructs can be made updatable by using an CREATE TABLE Project_tab ( Prj_level NUMBER, Projno NUMBER, Resp_dept NUMBER); CREATE TABLE Emp_tab ( Empno NUMBER NOT NULL, Ename VARCHAR2(10), Job VARCHAR2(9), Mgr NUMBER(4), Hiredate DATE, Sal NUMBER(7,2), Comm NUMBER(7,2), Deptno NUMBER(2) NOT NULL); CREATE TABLE Dept_tab ( Deptno NUMBER(2) NOT NULL, Dname VARCHAR2(14), Loc VARCHAR2(13), Mgr_no NUMBER, Dept_type NUMBER); CREATE OR REPLACE VIEW manager_info AS SELECT e.ename, e.empno, d.dept_type, d.deptno, p.prj_level, p.projno FROM Emp_tab e, Dept_tab d, Project_tab p WHERE e.empno = d.mgr_no AND d.deptno = p.resp_dept; CREATE OR REPLACE TRIGGER manager_info_insert INSTEAD OF INSERT ON manager_info REFERENCING NEW AS n -- new manager information FOR EACH ROW DECLARE rowcnt number; BEGIN SELECT COUNT(*) INTO rowcnt FROM Emp_tab WHERE empno = :n.empno; IF rowcnt = 0 THEN INSERT INTO Emp_tab (empno,ename) VALUES (:n.empno, :n.ename); ELSE UPDATE Emp_tab SET Emp_tab.ename = :n.ename WHERE Emp_tab.empno = :n.empno; END IF; SELECT COUNT(*) INTO rowcnt FROM Dept_tab WHERE deptno = :n.deptno; IF rowcnt = 0 THEN INSERT INTO Dept_tab (deptno, dept_type) VALUES(:n.deptno, :n.dept_type); ELSE UPDATE Dept_tab SET Dept_tab.dept_type = :n.dept_type WHERE Dept_tab.deptno = :n.deptno; END IF; SELECT COUNT(*) INTO rowcnt FROM Project_tab WHERE Project_tab.projno = :n.projno; IF rowcnt = 0 THEN INSERT INTO Project_tab (projno, prj_level) VALUES(:n.projno, :n.prj_level); ELSE UPDATE Project_tab SET Project_tab.prj_level = :n.prj_level WHERE Project_tab.projno = :n.projno; END IF; END; triggers can also be created over nested table view columns. CALL foo (ora_login_user) / CREATE OR REPLACE PROCEDURE Before_delete (Id IN NUMBER, Ename VARCHAR2) IS language Java name 'thjv Triggers.before Delete ( CHAR)'; CREATE OR REPLACE TRIGGER Pre_del_trigger BEFORE DELETE ON Tab FOR EACH ROW CALL Before_delete (:old. Ename) / Within a trigger body of a row trigger, the PL/SQL code and SQL statements have access to the old and new column values of the current row affected by the triggering statement.

These triggers provide a way of updating elements of the nested table. Two correlation names exist for every column of the table being modified: one for the old column value, and one for the new column value.

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