Question

我想在一个包含2个字段的结果表中显示2个查询。 wrong_answers和right_answers。

wrong_answers查询：

select count(ma_id) as wrong_answers
from exercicio natural
join avaliacao natural
join user_sessao
where se_id=4 and us_id=1 and not exists (
    select ma_id
    from grelha natural
    join exercicio natural
    join avaliacao natural
    join user_sessao
    where us_id=1 and se_id=4
)

right_answers查询：

select count(ma_id) as right_answers
from exercicio natural
join avaliacao natural
join user_sessao natural
join grelha where se_id=4 and us_id=1

当我wrong_answers查询UNION right_answers时，查询结果会显示在wrong_answers列中。

如何让它们成为2个差异列？

谢谢

Answer 1

在这种情况下，您不需要联合查询，如果您希望这些查询位于两个不同的列中，您可以使用：

SELECT
  (
    select count(ma_id) as wrong_answers
    from exercicio
    natural join avaliacao
    natural join user_sessao
    where se_id=4 and us_id=1 and not exists (
       select ma_id
       from grelha
       natural join exercicio
       natural join avaliacao
       natural join user_sessao
       where us_id=1 and se_id=4
    )
  ) AS wrong_answers,
  (
    select count(ma_id) as right_answers
    from exercicio
    natural join avaliacao
    natural join user_sessao
    natural join grelha
    where se_id=4 and us_id=1
  ) AS right_answers;

Answer 2

SELECT NULL AS correct, count(ma_id) AS wrong
.... wrong answer stuff here

UNION ALL

SELECT count(ma_id), NULL
.... right answer stuff here

Answer 3

UNION ALL保留两个结果集中的列。如果两个查询中都有一列，那么它将在最终结果集中出现一次。

使用UNION时有2个不同的字段

3 个答案: