Mysql database table cursor i have written the function below containing a cursor while executing it an error appears . what' wrong please

CREATE PROCEDURE processorders()
BEGIN
   DECLARE ordernumbers CURSOR FOR 
     SELECT * FROM psdms_feature_product 

   dept_rec ordernumbers%ROWTYPE
   o ordernumbers%ROWTYPE

   OPEN ordernumbers
   REPEAT
    FETCH ordernumbers INTO o

    IF (o.id_product ) THEN
      IF (o.id_feature  == 510) THEN
        update    psdms_feature_value_lang t1
        LEFT JOIN psdms_feature_product t2
        ON        t1.id_feature_value = t2.id_feature_value
        SET       value ='95090€'
        WHERE     t2.id_product = 1 
        AND       t2.id_feature = 510
      ELSE
        insert into psdms_feature_value ( id_feature ) values (510);
        insert into psdms_feature_product ( id_feature, id_product , id_feature_value) 
        values (o.id_feature , o.id_product , o.id_feature_value )
      END IF
    END IF

   UNTIL done END REPEAT
   CLOSE ordernumbers
END
END
Better is to avoid cursors.  Remember that SQL loves to do things in bulk, but hates to work with Cursors.

UPDATE  psdms_feature_value_lang t1
    JOIN  ordernumbers AS o  ON ...
    LEFT JOIN  psdms_feature_product t2
          ON t1.id_feature_value = t2.id_feature_value SET
    value  ='95090€'
    WHERE  t2.id_product = 1
      AND  t2.id_feature = 510
      AND  o.id_product
      AND  o.id_feature = 510;
INSERT
     INTO  psdms_feature_value ( id_feature ) 
SELECT  510
    FROM  ordernumbers
    WHERE  o.id_product
      AND  o.id_feature = 510;
INSERT
     INTO  psdms_feature_product ( id_feature, id_product, id_feature_value) 
SELECT  o.id_feature , o.id_product , o.id_feature_value
    FROM  ordernumbers
    WHERE  o.id_product
      AND  o.id_feature = 510;


Index:

ordernumbers: INDEX(id_feature, id_product, id_feature_value)


Other notes:

== is not proper syntax

What do you mean by AND id_product?  It probably tests for non-zero.