Question

update A set x = '0' where [condition];

if the where-condition isn’t fulfilled no update takes place.

depending on this I want to trigger an insert in another table, but only if an update was done – i.e. ROW_COUNT() > 0.

how may I do that in one request?

I tried this:

update A set x = '0' where [condition];

if row_count() > 0 then

  insert into [...];

end if;

this leads to an error.

PS:

The question is purely aming at a possibility to to execute an update and a conditional insert in one db-request. SQL-Injection-safty is assured by using prepared statements.

Answer 1

Create a stored procedure like:

DELIMITER $$

CREATE PROCEDURE updateA (c1 varchar)
BEGIN
  declare rows_affected integer;

  UPDATE a SET x = '0' WHERE col1 = c1;

  SELECT row_count() INTO rows_affected;

  IF rows_affected > 0 THEN BEGIN
    INSERT INTO .....
  END; END IF;

END $$

DELIMITER ;

Or use an AFTER UPDATE trigger

DELIMITER $$

CREATE TRIGGER au_a_each AFTER UPDATE ON a FOR EACH ROW
BEGIN
  INSERT INTO b (x,a_id) VALUES (new.x, new.id);
END $$

DELIMITER ;