Use trigger BEFORE INSERT on the table to prevent having a zero value in a MySQL field. Let us first create a table −
mysql> create table DemoTable(Value int); Query OK, 0 rows affected (0.85 sec)
Let us create a trigger to prevent having a zero value in a MySQL field −
mysql> DELIMITER // mysql> create trigger preventing_to_insert_zero_value before insert on DemoTable for each row begin if(new.Value = 0) then SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'You can not provide 0 value'; END if; end // Query OK, 0 rows affected (0.34 sec) mysql> DELIMITER ;
Let us insert 0 value in the table and check the value is going to be inserted or not. It won’t allow −
mysql> insert into DemoTable values(0); ERROR 1644 (45000): You cannot provide 0 value
So, in the above table, you cannot insert 0 value because of trigger. But, you can insert some other value.
Let us now insert some records in the table using insert command −
mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(-1000); Query OK, 1 row affected (0.41 sec)
Display all records from the table using select statement −
mysql> select *from DemoTable;
This will produce the following output −
+-------+ | Value | +-------+ | 10 | | -1000 | +-------+ 2 rows in set (0.00 sec)