Inconsistent behavior of the cursor

Question

I have a table 'dia'

and I have the function:

 create table log(
      cont int
 );

 delimiter //
 CREATE FUNCTION teste (calendario INT, data_selecionada DATE)
      RETURNS INT
 BEGIN

 DECLARE corrente INT DEFAULT 0;
 DECLARE data_inicio DATE DEFAULT NULL;
 DECLARE inicio INT DEFAULT 0;
 DECLARE maior_corrente INT DEFAULT 0;
 DECLARE existe_mais_linhas INT DEFAULT 0;
 DECLARE dia_atual DATE;
 DECLARE dia_anterior DATE DEFAULT NULL;
 DECLARE semana_atual INT DEFAULT -1;
 DECLARE semana_anterior INT DEFAULT -1;
 DECLARE total_vidas INT DEFAULT 0;
 DECLARE vidas INT DEFAULT 0;

 DECLARE meuCursor CURSOR FOR SELECT data, YEARWEEK(data), inicio_corrente FROM dia WHERE data >= data_selecionada and tem_corrente = 1 and calendario_id = calendario order by data asc;

 DECLARE CONTINUE HANDLER FOR NOT FOUND SET existe_mais_linhas=1;

 SELECT data into data_inicio FROM dia WHERE tem_corrente = 1 and inicio_corrente = 1 and data < data_selecionada order by data desc limit 1;

 OPEN meuCursor;

 meuLoop: LOOP
 FETCH meuCursor INTO dia_atual, semana_atual, inicio;
      insert into log (cont) values (1);

      IF existe_mais_linhas = 1 THEN
           LEAVE meuLoop;
      END IF;

 END LOOP meuLoop;

 CLOSE meuCursor;
 RETURN 0;

 END//
 delimiter ;

when I call the function:

 SELECT teste( 1,  '2014-01-26' )

the table log contains only one row... it's wrong, because the cursor have to visit all the nine rows... but, if i delete the line:

 SELECT data into data_inicio FROM dia WHERE tem_corrente = 1 and inicio_corrente = 1 and data < data_selecionada order by data desc limit 1;"

(The line is irrelevant, I think). But now, When I call the same function, the table log contains nine rows... how that line influences the loop??

Answer 1

The first query returned NO data.. so the variable is already SET and the program flow continued.. and since you refer it inside a loop before unsetting it.. instead of checking on no data for a cursor as you expected.!!

 SELECT data into data_inicio FROM dia WHERE tem_corrente = 1 and inicio_corrente = 1 and data < data_selecionada order by data desc limit 1;


 IF existe_mais_linhas = 1 THEN
    SET existe_mais_linhas = 0;-- unset it using SET..
  END IF;

 OPEN meuCursor;

 meuLoop: LOOP
 FETCH meuCursor INTO dia_atual, semana_atual, inicio;

      IF existe_mais_linhas = 1 THEN
           LEAVE meuLoop;
      END IF;

       -- Move the insert after checking it!

      insert into log (cont) values (1);

 END LOOP meuLoop;