SQL/MySQL/Trigger/NEW

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Change NEW value in a before insert trigger

   <source lang="sql">

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>

       </source>
   
  


Checking NEW value and create message

   <source lang="sql">
 

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 (0.08 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, 1 row affected (0.00 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, 1 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, 1 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, 1 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, 1 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, 1 row affected (0.01 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, 1 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, 1 row affected (0.00 sec) mysql> mysql> select * from Employee; +------+------------+-----------+------------+------------+---------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+------------+-----------+------------+------------+---------+-----------+-------------+ | 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | Programmer | | 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | Tester | | 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | Tester | | 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | Manager | | 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester | | 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | Tester | | 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | Manager | | 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | Tester | +------+------------+-----------+------------+------------+---------+-----------+-------------+ 8 rows in set (0.00 sec) mysql> mysql> mysql> mysql> delimiter $$ mysql> CREATE TRIGGER myTrigger

   ->   BEFORE UPDATE
   ->       ON employee
   ->      FOR EACH ROW
   -> BEGIN
   ->    DECLARE dummy INT;
   ->    IF NEW.salary<0 THEN
   ->       SELECT `Account balance cannot be less than 0` INTO dummy
   ->         FROM employee
   ->        WHERE id=NEW.id;
   ->   END IF;
   -> END$$

Query OK, 0 rows affected (0.02 sec) mysql> mysql> delimiter ; mysql> mysql> drop trigger myTrigger; Query OK, 0 rows affected (0.02 sec) mysql> mysql> mysql> mysql> update employee set salary = -1; Query OK, 8 rows affected (0.01 sec) Rows matched: 8 Changed: 8 Warnings: 0 mysql> mysql> drop table Employee; Query OK, 0 rows affected (0.00 sec) mysql> mysql> mysql>

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Reference new value with NEW in a "BEFORE UPDATE"

   <source lang="sql">

mysql> 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 (0.01 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, 1 row affected (0.00 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, 1 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, 1 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, 1 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, 1 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, 1 row affected (0.00 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, 1 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, 1 row affected (0.00 sec) mysql> mysql> select * from Employee; +------+------------+-----------+------------+------------+---------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+------------+-----------+------------+------------+---------+-----------+-------------+ | 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | Programmer | | 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | Tester | | 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | Tester | | 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | Manager | | 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester | | 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | Tester | | 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | Manager | | 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | Tester | +------+------------+-----------+------------+------------+---------+-----------+-------------+ 8 rows in set (0.00 sec) mysql> mysql> mysql> mysql> delimiter $$ mysql> CREATE TRIGGER myTrigger

   -> BEFORE UPDATE ON employee
   -> FOR EACH ROW
   -> BEGIN
   ->     IF NEW.salary <5000 THEN
   ->       SET NEW.first_name=CONCAT("NEW.first_name","*");
   ->     ELSE
   ->       SET NEW.last_name=CONCAT("NEW.last_name","*");
   ->     END IF;
   -> END$$

Query OK, 0 rows affected (0.00 sec) mysql> delimiter ; mysql> mysql> update employee set salary = 1000, first_name="new first Name"; Query OK, 8 rows affected (0.01 sec) Rows matched: 8 Changed: 8 Warnings: 0 mysql> mysql> select * from employee; +------+-----------------+-----------+------------+------------+---------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+-----------------+-----------+------------+------------+---------+-----------+-------------+ | 1 | NEW.first_name* | Martin | 1996-07-25 | 2006-07-25 | 1000.00 | Toronto | Programmer | | 2 | NEW.first_name* | Mathews | 1976-03-21 | 1986-02-21 | 1000.00 | Vancouver | Tester | | 3 | NEW.first_name* | Smith | 1978-12-12 | 1990-03-15 | 1000.00 | Vancouver | Tester | | 4 | NEW.first_name* | Rice | 1982-10-24 | 1999-04-21 | 1000.00 | Vancouver | Manager | | 5 | NEW.first_name* | Black | 1984-01-15 | 1998-08-08 | 1000.00 | Vancouver | Tester | | 6 | NEW.first_name* | Green | 1987-07-30 | 1996-01-04 | 1000.00 | New York | Tester | | 7 | NEW.first_name* | Larry | 1990-12-31 | 1998-02-12 | 1000.00 | New York | Manager | | 8 | NEW.first_name* | Cat | 1996-09-17 | 2002-04-15 | 1000.00 | Vancouver | Tester | +------+-----------------+-----------+------------+------------+---------+-----------+-------------+ 8 rows in set (0.00 sec) mysql> mysql> update employee set salary = 6000, last_name="new last Name"; Query OK, 8 rows affected (0.00 sec) Rows matched: 8 Changed: 8 Warnings: 0 mysql> mysql> select * from employee; +------+-----------------+----------------+------------+------------+---------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+-----------------+----------------+------------+------------+---------+-----------+-------------+ | 1 | NEW.first_name* | NEW.last_name* | 1996-07-25 | 2006-07-25 | 6000.00 | Toronto | Programmer | | 2 | NEW.first_name* | NEW.last_name* | 1976-03-21 | 1986-02-21 | 6000.00 | Vancouver | Tester | | 3 | NEW.first_name* | NEW.last_name* | 1978-12-12 | 1990-03-15 | 6000.00 | Vancouver | Tester | | 4 | NEW.first_name* | NEW.last_name* | 1982-10-24 | 1999-04-21 | 6000.00 | Vancouver | Manager | | 5 | NEW.first_name* | NEW.last_name* | 1984-01-15 | 1998-08-08 | 6000.00 | Vancouver | Tester | | 6 | NEW.first_name* | NEW.last_name* | 1987-07-30 | 1996-01-04 | 6000.00 | New York | Tester | | 7 | NEW.first_name* | NEW.last_name* | 1990-12-31 | 1998-02-12 | 6000.00 | New York | Manager | | 8 | NEW.first_name* | NEW.last_name* | 1996-09-17 | 2002-04-15 | 6000.00 | Vancouver | Tester | +------+-----------------+----------------+------------+------------+---------+-----------+-------------+ 8 rows in set (0.00 sec) mysql> mysql> drop trigger myTrigger; Query OK, 0 rows affected (0.00 sec) mysql> mysql> mysql> mysql> mysql> mysql> drop table Employee; Query OK, 0 rows affected (0.00 sec) mysql> mysql>

       </source>
   
  


Set NEW value to NULL in a before update trigger

   <source lang="sql">

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 (0.03 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, 1 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, 1 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, 1 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, 1 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, 1 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, 1 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, 1 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, 1 row affected (0.00 sec) mysql> mysql> select * from Employee; +------+------------+-----------+------------+------------+---------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+------------+-----------+------------+------------+---------+-----------+-------------+ | 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | Programmer | | 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | Tester | | 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | Tester | | 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | Manager | | 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester | | 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | Tester | | 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | Manager | | 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | Tester | +------+------------+-----------+------------+------------+---------+-----------+-------------+ 8 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<0 THEN
   ->      SET NEW.salary=NULL;
   ->   END IF;
   ->
   -> END$$

Query OK, 0 rows affected (0.00 sec) mysql> mysql> delimiter ; mysql> mysql> update employee set salary = -1; Query OK, 8 rows affected (0.00 sec) Rows matched: 8 Changed: 8 Warnings: 0 mysql> mysql> drop trigger myTrigger; Query OK, 0 rows affected (0.01 sec) mysql> mysql> select * from Employee; +------+------------+-----------+------------+------------+--------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+------------+-----------+------------+------------+--------+-----------+-------------+ | 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | NULL | Toronto | Programmer | | 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | NULL | Vancouver | Tester | | 3 | James | Smith | 1978-12-12 | 1990-03-15 | NULL | Vancouver | Tester | | 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | NULL | Vancouver | Manager | | 5 | Robert | Black | 1984-01-15 | 1998-08-08 | NULL | Vancouver | Tester | | 6 | Linda | Green | 1987-07-30 | 1996-01-04 | NULL | New York | Tester | | 7 | David | Larry | 1990-12-31 | 1998-02-12 | NULL | New York | Manager | | 8 | James | Cat | 1996-09-17 | 2002-04-15 | NULL | Vancouver | Tester | +------+------------+-----------+------------+------------+--------+-----------+-------------+ 8 rows in set (0.00 sec) mysql> mysql> mysql> drop table Employee; Query OK, 0 rows affected (0.00 sec) mysql> mysql> mysql>

       </source>