How Can I Enforce a Strict Row Limit in MySQL Tables?

Achieving Maximum Row Limits in MySQL Tables

The requirement to establish a strict maximum number of rows in MySQL tables poses a challenge, as the MAX_ROWS table property merely serves as a hint to the database engine. To enforce a hard limit, consider the following approaches:

Enforce Limit with Trigger

Create a BEFORE INSERT trigger to monitor row count:

DELIMITER $$

CREATE TRIGGER trigger1
BEFORE INSERT
ON table1
FOR EACH ROW
BEGIN
  SELECT COUNT(*) INTO @cnt FROM table1;
  IF @cnt >= 25 THEN
    CALL sth(); -- raise an error
  END IF;
END
$$

DELIMITER ;

Caution: COUNT operations on large InnoDB tables can be slow.

Raise Error on Overflow

Modify the trigger to explicitly raise an error when the limit is exceeded:

CREATE TRIGGER trigger1
BEFORE INSERT
ON table1
FOR EACH ROW
BEGIN
  DECLARE rowCount INT;
  SELECT COUNT(*) INTO rowCount FROM table1;

  IF (rowCount >= 25) THEN
    SIGNAL SQLSTATE '42000'
      SET MESSAGE_TEXT = 'Maximum row count reached (25)';
  END IF;
END

Performance Considerations

Note that frequent COUNT operations on large tables can impact performance. To mitigate this, consider optimizing the table and indexing it appropriately.

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