Error #1054 in MySQL Trigger

Question

This is my trigger.

DELIMITER //
CREATE TRIGGER verificare_masa
BEFORE INSERT ON Rezervare
FOR EACH ROW 
BEGIN
IF (NEW.Data_Rezervarii=Data_Rezervarii) AND (NEW.NumarMasa=NumarMasa) THEN 
    SET NEW.NumarMasa= NULL;

END IF;
END //
DELIMITER ;

I want to make trigger on 1 table (rezervare).

When I execute the trigger, it has been created. But, when I insert data into table rezervare, It become Error Code: 1054. Unknown column 'Data_Rezervarii' in 'field list'

I want to check if a reservation is already in the data base for that date and mass required is already reserved for that date

Answer 1

From your attempt, it appears that you want to still insert a new row with the same Data_Rezervarii , but with NumarMasa NULL . If so, your trigger should be something like

CREATE TRIGGER verificare_masa 
BEFORE INSERT ON Rezervare FOR EACH ROW 
SET NEW.NumarMasa = IF(EXISTS(
  SELECT 1 FROM Rezervare 
  WHERE Data_Rezervarii=NEW.Data_Rezervarii 
    AND NumarMasa = NEW.NumarMasa
  ),NULL,NEW.NumarMasa);

Then it would work like this:

MariaDB [test]> select * from Rezervare;
+-----------------+-----------+
| Data_Rezervarii | NumarMasa |
+-----------------+-----------+
| 2016-12-12      |         1 |
| 2016-12-12      |         2 |
| 2016-12-13      |         3 |
+-----------------+-----------+
3 rows in set (0.00 sec)

MariaDB [test]> INSERT INTO Rezervare VALUES ('2016-12-12',1),('2016-12-12',4);
Query OK, 2 rows affected (0.20 sec)
Records: 2  Duplicates: 0  Warnings: 0

MariaDB [test]> select * from Rezervare;
+-----------------+-----------+
| Data_Rezervarii | NumarMasa |
+-----------------+-----------+
| 2016-12-12      |         1 |
| 2016-12-12      |         2 |
| 2016-12-13      |         3 |
| 2016-12-12      |      NULL |
| 2016-12-12      |         4 |
+-----------------+-----------+
5 rows in set (0.00 sec)

But if you actually want to skip the new record completely if one already exists in the table, it should be done by adding a unique index on these two columns and using INSERT IGNORE .