update table column after insert new record using MySQL triggers

Question

Imagine I have a MySQL table (tbl_test) with these fields: id, title, priority.
id will be incremented automatically. I need to fill

Answer 1

I don't think you can do that. An AFTER INSERT trigger cannot modify the same table, neither by issuing an UPDATE nor by something like this:

DROP TRIGGER new_tbl_test;

DELIMITER $$

CREATE TRIGGER new_tbl_test 
AFTER INSERT ON tbl_test for each row
begin
UPDATE tbl_test SET priority = new.id WHERE id = new.id;
END $$

DELIMITER ;

It gives error like

ERROR 1442 (HY000): Can't update table 'tbl_test' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.

---

What you can do, is use a transaction:

Example : Table structure is like below

mysql> show create table tbl_test\G
*************************** 1. row ***************************
       Table: tbl_test
Create Table: CREATE TABLE `tbl_test` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `title` char(30) DEFAULT NULL,
  `priority` int(11) DEFAULT NULL,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

Transaction

START TRANSACTION ;
  INSERT INTO tbl_test (title)
    VALUES ('Dr');
  UPDATE tbl_test
    SET `priority` = id
    WHERE id = LAST_INSERT_ID();
COMMIT ;

Check data

mysql> SELECT * FROM tbl_test;
+----+-------+----------+
| ID | title | priority |
+----+-------+----------+
|  1 | Dr    |        1 |
+----+-------+----------+
1 row in set (0.00 sec)