Multiple cursors in nested loops in MySQL

问题:

I wish to do something which appear a bit complicated in MySQL. In fact, I wish to open a cursor, do a loop, and in this loop, open a second cursor using the data from the previous fetch to be executed, and re-loop on the results.

  DECLARE idind INT;
  DECLARE idcrit INT;
  DECLARE idindid INT;
  DECLARE done INT DEFAULT 0;
  DECLARE done2 INT DEFAULT 0;
  DECLARE curIndicateur CURSOR FOR SELECT id_indicateur FROM indicateur;
  DECLARE curCritereIndicateur CURSOR FOR SELECT C.id_critere FROM critere C where C.id_indicateur=idind;
  DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1;

  set idindid=54;
  OPEN curIndicateur;
  REPEAT
    FETCH curIndicateur INTO idind;
    open curCritereIndicateur;
    REPEAT
      FETCH curIndicateur INTO idcrit;
      INSERT INTO SLA_DEMANDE_STATUS (iddemande,idindicateur,indicateur_status,progression) values('0009',idcrit,'OK',10.0);
    UNTIL done END REPEAT;
    close curCritereIndicateur;
  UNTIL done END REPEAT;
  CLOSE curIndicateur;

In fact, how to do 'Until done' differently for the two cursors, because you can only declare one handler for SQLSTATE? If the first ends, the second ends too.

回答1:

You need to define a new BLOCK inside your 1st cursor loop and use different Declares in that block.

Something like:

BLOCK1: begin
    declare v_col1 int;                     
    declare no_more_rows boolean1 := FALSE;  
    declare cursor1 cursor for              
        select col1
        from   MyTable;
    declare continue handler for not found  
        set no_more_rows1 := TRUE;           
    open cursor1;
    LOOP1: loop
        fetch cursor1
        into  v_col1;
        if no_more_rows1 then
            close cursor1;
            leave LOOP1;
        end if;
        BLOCK2: begin
            declare v_col2 int;
            declare no_more_rows2 boolean := FALSE;
            declare cursor2 cursor for
                select col2
                from   MyOtherTable
                where  ref_id = v_col1;
           declare continue handler for not found
               set no_more_rows2 := TRUE;
            open cursor2;
            LOOP2: loop
                fetch cursor2
                into  v_col2;
                if no_more_rows then
                    close cursor2;
                    leave LOOP2;
                end if;
            end loop LOOP2;
        end BLOCK2;
    end loop LOOP1;
end BLOCK1;

回答2:

Correct me if I'm wrong, but it looks like what you are trying to do is a bulk insert of records into your "SLA_DEMANDE_STATUS" table. Include every criteria for every indicator found and default it with the values of '0009', 'OK' and 10.0 per each indicator's Criteria ID.

This can all be done in a single SQL-Insert. INSERT INTO ... from a SQL-Select...

Now, if you want to only include a single "id_indicateur" entry, you can add that to the WHERE clause of the select statement.

Notice that my SQL-Select has forced values to correspond with the columns you want to have populated. They will all be inserted to the destination table by the same name. The nice thing about this, you can just run the SQL-SELECT portion just to see the data you would EXPECT to have inserted... if its incorrect, you can adjust it to fit whatever restrictions you want.

insert into SLA_DEMANDE_STATUS 
    ( iddemande,
      idindicateur,
      indicateur_status,
      progression ) 
    SELECT 
         '0009' iddemande,
         c.id_criterere idindicateur,
         'OK' indicateur_status,
         10.0 progression
       FROM 
          indicateur i;
             JOIN critere c
                ON i.id_indicateur = c.id_indicateur

回答3:

you could use loop,and reset the value of the handle,like this:

get_something:loop
  open cur;
  fetch cur into temp_key;
  if no_more_record=1 then
    set no_more_record=0;
    close cur;
    leave get_something;
  else
    //do your job;
  end if;
end loop;

回答4:

Or redefine the CONTINUE HANDLE:

//...
LOOP1: LOOP
      fetch cursor1
      into  v_col1;
      if no_more_rows1 then
         close cursor1;
         leave LOOP1;
      end if;
//...

      SET no_more_rows1=false;//That's new
END LOOP LOOP1;          

It seems that all select statements inside a loop execute the CONTINUE HANDLE

回答5:

DECLARE _idp INT;
DECLARE _cant INT;
DECLARE _rec INT;
DECLARE done INT DEFAULT 0;
-- Definición de la consulta
DECLARE primera CURSOR FOR SELECT dp.id_prod, SUM(dp.cantidad) AS cantidad, pp.receta FROM tm_detalle_pedido AS dp INNER JOIN tm_producto_pres AS pp
DECLARE segunda CURSOR FOR SELECT id_ins, cant FROM tm_producto_ingr WHERE id_pres = _idp;

-- Declaración de un manejador de error tipo NOT FOUND
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

-- Abrimos el primer cursor
OPEN primera;

REPEAT

FETCH primera INTO _idp, _cant, _rec;

IF NOT done THEN

 OPEN segunda;
 block2: BEGIN
     DECLARE doneLangLat INT DEFAULT 0;
     DECLARE _ii INT;
     DECLARE i FLOAT;
     DECLARE _canti FLOAT;
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET doneLangLat = 1;

     REPEAT
     FETCH segunda INTO _ii,_canti;
     IF NOT doneLangLat THEN
        IF _rec = 1 THEN
            SET i = _canti * _cant;
            -- Insertamos
            INSERT INTO tm_inventario (id_ins,id_tipo_ope,id_cv,cant,fecha_r) 
            VALUES (_ii, 2, @id, i, _fecha);
        END IF;
     END IF;
     UNTIL doneLangLat END REPEAT;

  END block2;
  CLOSE segunda;

 END IF;

 UNTIL done END REPEAT;
 CLOSE primera;