#
# Oracle Performance Tuning Chapter 10 p. 197
#
# SELECT...FOR UPDATE OF: Locking a Row Explicitly
    TRIGGER ON-LOCK
#
    SELECT  'X' 
        FROM  EMP 
        WHERE EMP_NO = 1234 
        FOR UPDATE OF EMP_NO;
#
    SELECT  X' 
        FROM  EMP_HISTORY
        WHERE EMP_NO = 1234 
        FOR UPDATE OF EMP_NO;
#
# Oracle Performance Tuning Chapter 10 p. 200
#
# SELECT...FOR UPDATE OF: Locking a Row Explicitly
#
#Using Pseudo-code to Lock a Large Table
    DECLARE 
       CURSOR C1   IS
           SELECT  EMP_NO 
               FROM  EMP
               WHERE EMP_DEPT = 0020;
    CURSOR C2 IS
        SELECT ROWID 
            FROM   EMP
             WHERE EMP_NO   = :XEMP_NO
            AND    EMP_DEPT  = 0020
            FOR    UPDATE OF . . .;

    BEGIN
        KOUNTER = 0;
        OPEN C1;
        
        BEGIN_LOOP;
            FETCH C1 INTO :XEMP_NO;
        
            OPEN C2;
            FETCH C2 INTO :XROWID;

            IF C2%FOUND THEN
                UPDATE EMP
                SET  . . . =  . . .
                WHERE  ROWID = :XROWID
                KOUNTER = KOUNTER + 1;
                IF   KOUNTER = 20   THEN
                     COMMIT;
                     KOUNTER = 0;
                END IF;
            END IF;
        END_LOOP;

        CLOSE C1;
        CLOSE C2;
    END;