请编写触发器：每当在EMPLOYEES表中插入一行数据时，相应部门的职工总人数就加1。

本题考察了后触发器的编写。创建DML触发器的一般语法是：

CREATE [OR REPLACE] TRIGGER trigger_name

{BEFORE | AFTER }

{INSERT | DELETE | UPDATE [OF column [, column …]]}

ON [schema.] table_name

[REFERENCING {OLD [AS] old | NEW [AS] new| PARENT as parent}]

[FOR EACH ROW ]

[WHEN condition]

trigger_body;

BEFORE和AFTER指出触发器的触发时机为前触发还是后触发，前触发是在执行触发事件之前触发，后触发是在执行触发事件之后触发当前所创建的触发器。最终触发器如下所示：

CREATE TRIGGER INSERT_TRIGGER

  AFTER INSERT ON EMPLOYEES

BEGIN

  UPDATE DEPARTMENTS T

     SET T.TOTALNUMBER = T.TOTALNUMBER + 1

   WHERE T.DEPTNO = :NEW.DEPTNO;

END;