Set NEW value to NULL in a before update trigger : NEW « Trigger « SQL / MySQL

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SQL / MySQL » Trigger » NEW 
Set NEW value to NULL in a before update trigger
 
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, rows affected (0.03 sec)

mysql>
mysql>
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');
Query OK, row affected (0.02 sec)

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');
Query OK, row affected (0.00 sec)

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');
Query OK, row affected (0.00 sec)

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');
Query OK, row affected (0.00 sec)

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');
Query OK, row affected (0.00 sec)

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');
Query OK, row affected (0.02 sec)

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');
Query OK, row affected (0.00 sec)

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');
Query OK, row affected (0.00 sec)

mysql>
mysql> select from Employee;
+------+------------+-----------+------------+------------+---------+-----------+-------------+
| id   | first_name | last_name | start_date | end_date   | salary  | city      | description |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
|    | Jason      | Martin    | 1996-07-25 2006-07-25 1234.56 | Toronto   | Programmer  |
|    | Alison     | Mathews   | 1976-03-21 1986-02-21 6661.78 | Vancouver | Tester      |
|    | James      | Smith     | 1978-12-12 1990-03-15 6544.78 | Vancouver | Tester      |
|    | Celia      | Rice      | 1982-10-24 1999-04-21 2344.78 | Vancouver | Manager     |
|    | Robert     | Black     | 1984-01-15 1998-08-08 2334.78 | Vancouver | Tester      |
|    | Linda      | Green     | 1987-07-30 1996-01-04 4322.78 | New York  | Tester      |
|    | David      | Larry     | 1990-12-31 1998-02-12 7897.78 | New York  | Manager     |
|    | James      | Cat       | 1996-09-17 2002-04-15 1232.78 | Vancouver | Tester      |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
rows in set (0.00 sec)

mysql>
mysql>
mysql>
mysql>
mysql> delimiter $$
mysql>
mysql> CREATE TRIGGER myTrigger
    ->  BEFORE UPDATE ON employee FOR EACH ROW
    -> BEGIN
    ->   DECLARE dummy INT;
    ->
    ->   IF NEW.salary<THEN
    ->      SET NEW.salary=NULL;
    ->   END IF;
    ->
    -> END$$
Query OK, rows affected (0.00 sec)

mysql>
mysql> delimiter ;
mysql>
mysql> update employee set salary = -1;
Query OK, rows affected (0.00 sec)
Rows matched: 8  Changed: 8  Warnings: 0

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

mysql>
mysql> select from Employee;
+------+------------+-----------+------------+------------+--------+-----------+-------------+
| id   | first_name | last_name | start_date | end_date   | salary | city      | description |
+------+------------+-----------+------------+------------+--------+-----------+-------------+
|    | Jason      | Martin    | 1996-07-25 2006-07-25 |   NULL | Toronto   | Programmer  |
|    | Alison     | Mathews   | 1976-03-21 1986-02-21 |   NULL | Vancouver | Tester      |
|    | James      | Smith     | 1978-12-12 1990-03-15 |   NULL | Vancouver | Tester      |
|    | Celia      | Rice      | 1982-10-24 1999-04-21 |   NULL | Vancouver | Manager     |
|    | Robert     | Black     | 1984-01-15 1998-08-08 |   NULL | Vancouver | Tester      |
|    | Linda      | Green     | 1987-07-30 1996-01-04 |   NULL | New York  | Tester      |
|    | David      | Larry     | 1990-12-31 1998-02-12 |   NULL | New York  | Manager     |
|    | James      | Cat       | 1996-09-17 2002-04-15 |   NULL | Vancouver | Tester      |
+------+------------+-----------+------------+------------+--------+-----------+-------------+
rows in set (0.00 sec)

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

mysql>
mysql>
mysql>

        
Related examples in the same category
1.Reference new value with NEW in a 'BEFORE UPDATE'
2.Change NEW value in a before insert trigger
3.Checking NEW value and create message
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