Nested Cursors in Mysql

Question

I have three tables.
Project(Id), attribute(Id), project_attribute(Id, project_id, attribute_id).

I want to create records in project_at

Answer 1

After the first iteration within the inner cursor "attribute_done" variable is set to "true". And it remains "true" for every next iterations.

This causes every next iterations to skip the inner loop.

A sample nested cursor is illustrated below.

---

CREATE TABLE `parent` (
  `a` int(11) DEFAULT NULL
) ENGINE=InnoDB
CREATE TABLE `child` (
  `a` int(11) DEFAULT NULL,
  `b` varchar(20) DEFAULT NULL
) ENGINE=InnoDB

insert into parent values (1),(2),(3);

insert into child values (1,'a'),(1,'b'),(2,'a'),(2,'b'),(3,'a'),(3,'b');

----------------------------------
drop procedure if exists nestedCursor;
create procedure nestedCursor()
BEGIN   
    DECLARE done1, done2 BOOLEAN DEFAULT FALSE;  
    DECLARE parentId,childId int;
    DECLARE childValue varchar(30);

    DECLARE cur1 CURSOR FOR SELECT a FROM parent;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done1 = TRUE;

    open cur1;
    loop1: LOOP
    FETCH FROM cur1 INTO parentId;
    IF done1 THEN
        CLOSE cur1;
        LEAVE loop1;
    END IF;

    BLOCK1 : BEGIN
    DECLARE cur2 CURSOR FOR SELECT a,b FROM child where a = parentId;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done2 = TRUE;


    open cur2;
    loop2 : LOOP
    FETCH FROM cur2 INTO childId,childValue;  
        if done2 THEN
        CLOSE cur2;
        SET done2 = FALSE;
        LEAVE loop2;
        end if;
        select parentId,childId,childValue;

    END LOOP loop2;
    END BLOCK1;
    END loop loop1;
END;