mysql - 使用 UNION 时有 2 个不同的字段

Question

我想让 2 个查询出现在一个具有 2 个字段的结果表中。错误答案和正确答案。

错误答案查询:

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
)

正确答案查询:

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

当我执行 wrong_answers 查询 UNION right_answers 查询时，两个结果都会显示在错误的_answers 列中。

如何使它们成为 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;