PHP-如何在这两个查询上全部使用UNION

Question

I want to merge those queries in one, using union all, how can i do that?

$query = ("SELECT menu_id, menu_friendlyName
        FROM menu
        WHERE back = 1 AND active = 1")


$query = ("SELECT menu_id, submenu_id, submenu_name, url
        FROM submenu
        WHERE active = 1");

Answer 1

For example this way:

$query =
  "select * from (
   SELECT
      menu_id,
      menu_friendlyName,
      NULL as submenu_id,
      NULL as url,
   FROM menu
   WHERE back = 1 AND active = 1
    union all 
   SELECT
      menu_id,
      NULL as menu_friendlyName,
      submenu_id,
      submenu_name,
      url,
   FROM submenu
   WHERE active = 1) x"
);

Otherwise as others mentioned the union doesn't really look a good idea.

Answer 2

If you want to select menu entries with corresponding submenu entries you have to use JOIN instead. I would use LEFT JOIN for this:

SELECT m.menu_id, m.menu_friendlyName, s.submenu_id, s.submenu_name, s.url
FROM menu AS m
LEFT JOIN submenu AS s
    ON s.menu_id = m.menu_id
WHERE
    m.back = 1
    AND m.active = 1
    AND s.active = 1

If you use JOIN , the query returns menu entries, which have at least one submenu entry. If you use LEFT JOIN , it returns also menu entries without any submenu entry.