Change NEW value in a before insert trigger : NEW « Trigger « MySQL Tutorial

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2. Trigger
3. NEW

mysql>
mysql>
mysql> CREATE TABLE Employee(
    ->     id            int,
    ->     first_name    VARCHAR(15),
    ->     last_name     VARCHAR(15),
    ->     start_date    DATE,
    ->     end_date      DATE,
    ->     salary        FLOAT(8,2),
    ->     city          VARCHAR(10),
    ->     description   VARCHAR(15)
    -> );
Query OK, 0 rows affected (0.02 sec)

mysql>
mysql>
mysql> delimiter $$
mysql>
mysql> CREATE TRIGGER myTrigger
    ->   BEFORE INSERT ON employee
    ->   FOR EACH ROW
    -> BEGIN
    ->   DECLARE row_count INTEGER;
    ->
    ->   SELECT COUNT(*)
    ->     INTO row_count
    ->     FROM employee
    ->    WHERE id=NEW.id;
    ->
    ->   IF row_count > 0 THEN
    ->     UPDATE employee
    ->        SET salary = salary+NEW.salary
    ->      WHERE id=NEW.id;
    ->   ELSE
    ->     INSERT INTO employee (id,salary) VALUES(NEW.id,NEW.salary);
    ->   END IF;
    ->
    -> END$$
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> delimiter ;
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->              values (1,'Jason',    'Martin',  '19960725',  '20060725', 1234.56, 'Toronto',  'Programmer');
ERROR 1442 (HY000): Can't update table 'employee' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(2,'Alison',   'Mathews',  '19760321', '19860221', 6661.78, 'Vancouver','Tester');
ERROR 1442 (HY000): Can't update table 'employee' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(3,'James',    'Smith',    '19781212', '19900315', 6544.78, 'Vancouver','Tester');
ERROR 1442 (HY000): Can't update table 'employee' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(4,'Celia',    'Rice',     '19821024', '19990421', 2344.78, 'Vancouver','Manager');
ERROR 1442 (HY000): Can't update table 'employee' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(5,'Robert',   'Black',    '19840115', '19980808', 2334.78, 'Vancouver','Tester');
ERROR 1442 (HY000): Can't update table 'employee' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(6,'Linda',    'Green',    '19870730', '19960104', 4322.78,'New York',  'Tester');
ERROR 1442 (HY000): Can't update table 'employee' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(7,'David',    'Larry',    '19901231', '19980212', 7897.78,'New York',  'Manager');
ERROR 1442 (HY000): Can't update table 'employee' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(8,'James',    'Cat',     '19960917',  '20020415', 1232.78,'Vancouver', 'Tester');
ERROR 1442 (HY000): Can't update table 'employee' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql>
mysql> select * from Employee;
Empty set (0.00 sec)

mysql>
mysql>
mysql>
mysql>
mysql> drop trigger myTrigger;
Query OK, 0 rows affected (0.01 sec)

mysql>
mysql>
mysql>
mysql>
mysql>
mysql> drop table Employee;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>