选择NULL列

Question

我编写了一个查询，它正在选择有时为NULL的列。

$q = "SELECT g.id AS gameid,g.home_user, g.home_user2, g.away_user, g.away_user2, g.home_score, g.away_score, g.date_confirmed, g.type,
          h1.username AS home_username, h2.username AS home_username2, a1.username AS away_username2, a2.username AS away_username2
          FROM ".TBL_FOOT_GAMES." g 
          INNER JOIN ".TBL_USERS." h1 ON h1.id = g.home_user
          INNER JOIN ".TBL_USERS." h2 ON h2.id = g.home_user2
          INNER JOIN ".TBL_USERS." a1 ON a1.id = g.away_user
          INNER JOIN ".TBL_USERS." a2 ON a2.id = g.away_user2
          WHERE g.status = '$status'
          ORDER BY g.date_confirmed DESC LIMIT 25";

列

  

home_user2和away_user2

有时可以为NULL。显然，这似乎阻止查询显示任何返回的数据。 当我从查询中删除这些列时，我得到了一个返回。 包括它们不会引发错误，只是简单就是不选择任何行。

我怎样才能解决这个问题？

Answer 1

您需要使用left join，而不是这些列上的内部联接。

$q = "SELECT g.id AS gameid,g.home_user, g.home_user2, g.away_user, g.away_user2, g.home_score, g.away_score, g.date_confirmed, g.type,
          h1.username AS home_username, h2.username AS home_username2, a1.username AS away_username2, a2.username AS away_username2
          FROM ".TBL_FOOT_GAMES." g 
          INNER JOIN ".TBL_USERS." h1 ON h1.id = g.home_user
          LEFT JOIN ".TBL_USERS." h2 ON h2.id = g.home_user2
          INNER JOIN ".TBL_USERS." a1 ON a1.id = g.away_user
          LEFT JOIN ".TBL_USERS." a2 ON a2.id = g.away_user2
          WHERE g.status = '$status'
          ORDER BY g.date_confirmed DESC LIMIT 25";