求详细解答，谢谢。经验不充足，希望大神多多教学

1 创建table1:

CREATE TABLE table1 
( id number(5), 
  name char(20), 
  age number(2), 
);

2 创建table2,并给count字段初值为0

CREATE TABLE table2 
( count number(5), 
);

INSERT INTO table2 VALUES (0);

3 插入触发器

CREATE OR REPLACE TRIGGER add_after_insert
AFTER INSERT
   ON table1
   FOR EACH ROW

DECLARE
   v_currentCount number(5); 

BEGIN
    SELECT count INTO v_currentCount FROM table2;
    UPDATE table2  SET count = v_currentCount +1;
END

4 删除触发器

CREATE OR REPLACE TRIGGER add_after_delete
AFTER DELETE
   ON table1
   FOR EACH ROW

DECLARE
   v_currentCount number(5); 

BEGIN
    SELECT count INTO v_currentCount FROM table2;
    UPDATE table2  SET count = v_currentCount +1;
END

5 更新触发器

CREATE OR REPLACE TRIGGER add_after_update
AFTER UPDATE
   ON table1
   FOR EACH ROW

DECLARE
   v_currentCount number(5); 

BEGIN
    SELECT count INTO v_currentCount FROM table2;
    UPDATE table2  SET count = v_currentCount +1;
END

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