CREATE TABLE tbl1 (
      mem_id MEDIUMINT UNSIGNED NOT NULL,
      cat CHAR(3) NOT NULL,
      item_id SMALLINT UNSIGNED NOT NULL,
);

CREATE TABLE tbl2 (
      cat CHAR(3) NOT NULL,
      item_id MEDIUMINT UNSIGNED NOT NULL,
      item TINYTEXT NOT NULL,
);

CREATE TABLE tbl3 (
      mem_id MEDIUMINT UNSIGNED NOT NULL,
      cat CHAR(3) NOT NULL,
      item_id MEDIUMINT UNSIGNED NOT NULL,
      selected TINYTEXT NOT NULL,
);

#tbl1
INSERT INTO tbl1 VALUES ('1', '201', '1');
INSERT INTO tbl1 VALUES ('1', '201', '3');
INSERT INTO tbl1 VALUES ('2', '201', '1');
INSERT INTO tbl1 VALUES ('2', '201', '2');
INSERT INTO tbl1 VALUES ('3', '201', '1');

#tbl2
INSERT INTO tbl2 VALUES ('201', '1', 'this is item1');
INSERT INTO tbl2 VALUES ('201', '2', 'this is item2');
INSERT INTO tbl2 VALUES ('201', '3', 'this is item3');

#tbl3
INSERT INTO tbl3 VALUES ('1', '201', '1', 'selected1');
INSERT INTO tbl3 VALUES ('2', '201', '2', 'selected2');

SELECT tbl1.mem_id, tbl1.cat, item, selected
  FROM tbl1
  LEFT JOIN tbl3 USING (mem_id, cat, item_id)
  LEFT JOIN tbl2 USING (cat, item_id)
  WHERE tbl1.mem_id=2

mem_id cat  item              selected
2      201   NULL             NULL
2      201   this is item2    selected2

mem_id cat  item              selected
2      201   this is item1    NULL
2      201   this is item2    selected2

select tbl1.mem_id    as mem1
     , tbl1.cat       as cat1 
     , tbl1.item_id   as item1
     , tbl3.mem_id    as mem3
     , tbl3.cat       as cat3
     , tbl3.item_id   as item3
     , tbl3.selected
     , tbl2.cat       as cat2
     , tbl2.item_id   as item2 
     , tbl2.item
  from tbl1
left outer
  join tbl3 
    on tbl1.mem_id  = tbl3.mem_id
   and tbl1.cat     = tbl3.cat
   and tbl1.item_id = tbl3.item_id
left outer
  join tbl2 
   on  tbl1.cat     = tbl2.cat
   and tbl1.item_id = tbl2.item_id
 where tbl1.mem_id=2

mem1 cat1 item1 mem3 cat3 item3 selected  cat2 item2 item
  2  201    1   NULL NULL NULL  NULL      201    1   this is item1
  2  201    2    2   201   2    selected2 201    2   this is item2

mem1 cat1 item1 mem3 cat3 item3 selected  cat2 item2 item
  2  201    1   NULL NULL NULL  NULL      NULL NULL  NULL
  2  201    2    2   201  2     selected2 201    2   this is item2