How to limit number of rows can be store in mysql table?

Question

I need to limit the number of rows can be insert in a MySQL Table to 10 only. I need to implement this from MySQL only i.e without using any programming lan

Answer 1

I think there is no such inbuilt functionality providede by MySQL. One solution is that you can create trigger.

CREATE TRIGGER your_trigger_name
BEFORE INSERT ON your_table_name
FOR EACH ROW
BEGIN
    DECLARE cnt INT;

    SELECT count(*) INTO cnt FROM your_table_name;

    IF cnt = 10 THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'You can store only 10 records.';
    END IF;
END;

Try above trigger on your table. Replace your table_name with your_table_name.

Hope this will help you.

Answer 2

As check constraint does not seems to work with MySql. You can try creating a BEFORE INSERT TRIGGER on your table and set NEW.column value as NULL for some not nullable column to break the insert statement.

Ex:  
CREATE TABLE mytable (
    id INT NOT NULL,
    col1 VARCHAR(255) NOT NULL,
    col2 VARCHAR(255),
);  

DELIMITER $$
CREATE TRIGGER mytable_before_trig BEFORE INSERT ON mytable
FOR EACH ROW
BEGIN 
IF (SELECT COUNT(id) FROM mytable) > 3 THEN
    SET NEW.id = NULL;
END IF;
END;
$$  

Now try to insert records in mytable, it will ignore 4th records by throwing an error.

Answer 3

Here's one idea...:

CREATE TABLE my_table
(id int auto_increment PRIMARY KEY  
,val char(1) NOT NULL
);

INSERT INTO my_table (val) SELECT 'b' FROM (SELECT 1) x WHERE (SELECT COUNT(*) FROM my_table) < 5;
Query OK, 1 row affected (0.02 sec)

INSERT INTO my_table (val) SELECT 'b' FROM (SELECT 1) x WHERE (SELECT COUNT(*) FROM my_table) < 5;
Query OK, 1 row affected (0.02 sec)

INSERT INTO my_table (val) SELECT 'b' FROM (SELECT 1) x WHERE (SELECT COUNT(*) FROM my_table) < 5;
Query OK, 1 row affected (0.02 sec)

INSERT INTO my_table (val) SELECT 'b' FROM (SELECT 1) x WHERE (SELECT COUNT(*) FROM my_table) < 5;
Query OK, 1 row affected (0.02 sec)

INSERT INTO my_table (val) SELECT 'b' FROM (SELECT 1) x WHERE (SELECT COUNT(*) FROM my_table) < 5;
Query OK, 1 row affected (0.02 sec)

INSERT INTO my_table (val) SELECT 'b' FROM (SELECT 1) x WHERE (SELECT COUNT(*) FROM my_table) < 5;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

INSERT INTO my_table (val) SELECT 'b' FROM (SELECT 1) x WHERE (SELECT COUNT(*) FROM my_table) < 5;
Query OK, 0 rows affected (0.00 sec)

SELECT * FROM my_table;
+----+-----+
| id | val |
+----+-----+
|  1 | b   |
|  2 | b   |
|  3 | b   |
|  4 | b   |
|  5 | b   |
+----+-----+