How to issue such sql-query?

Question

SQL

There are two tables:
main :
_____________________
| PROD |  LIST_ID   |
-----------------------  
| a | 3 |
-----------------------
| a | 4 |
-----------------------
| b | 1 |
-----------------------
list :
_____________________
|   ID    | LIST_VAL |
-----------------------
| 1 | 11 |
-----------------------
| 2 | 22 |
-----------------------
| 3 | 33 |
-----------------------
| 4 | 44 |
------------------------
You need to take all the lines from list and join them with each line from main (on the fields  main.LIST_ID  and  list.ID ) and get the following:
_________________________________
| PROD | LIST_ID | LIST_VAL |
--------------------------------------  
| a | 1 | null |
--------------------------------------
| a | 2 | null |
--------------------------------------
| a | 3 | 33 |
--------------------------------------
| a | 4 | 44 |
----------------------------------------------------
| b | 1 | 11 |
--------------------------------------
| b | 2 | null |
--------------------------------------
| b | 3 | null |
--------------------------------------
| b | 4 | null |
--------------------------------------

Answer 1

select l.prod, l.id list_id, l.list_val from list l left join main m on <Дальше сам>

Answer 2

SELECT `p`.`PROD` AS `PROD`, `l`.`ID` AS `LIST_ID`,
       IF(`m`.`PROD` IS NULL, NULL, `l`.`LIST_VAL`) AS `LIST_VAL`
  FROM (
    SELECT DISTINCT `PROD`
      FROM `main`
  ) AS `p`
  JOIN `list` AS `l`
  LEFT JOIN `main` AS `m`
    ON `m`.`PROD` = `p`.`PROD` AND `m`.`LIST_ID` = `l`.`ID`
  ORDER BY `p`.`PROD`, `l`.`ID`