Question

我无法进行查询以获得某些交叉值。我对mysql的了解不太适合制作这类东西。

我有两个表，signedup和signedupLocal。两个字段相同：name，surname1，surname2，NIF，year，city，status和dateSigned。

我希望在surname1和surname2（A到Z）排序的状态为0时，将两个表中的所有值组合在一起。另外，我想要一个名为“app”的新字段，根据数据来自哪个表，它会显示是或否。如果是signedpupLocal，则是其他没有。

之后，当dateSigned（旧的第一个）命令状态为1时，我想做同样的事情。

到目前为止，我还没有尝试过测试一个完整的查询，因为我只有一部分问题。

我已尝试过类似的内容：

SELECT signedupLocal.name,
       signedupLocal.surname1, 
       signedupLocal.surname2,
       signedupLocal.NIF,
       signedupLocal.year, 
       signedupLocal.city, 
       signedup.name, 
       signedup.surname1, 
       signedup.surname2, 
       signedup.NIF, 
       signedup.year, 
       signedup.city  
FROM signedup, signedupLocal
WHERE signedup.id_Event = 78 
AND signedupLocal.id_Event = 78
AND signedupLocal.status = 0
AND signedup.status = 0

但它失败了。

Answer 1

SELECT name, surname1, surname2, NIF, year, city, status, 'no' as app,
       case when status = 1 then datesigned else '2099-12-31' end as datesigned_sort,
       case when status = 0 then surname1 else '' end as surname1_sort,
       case when status = 0 then surname2 else '' end as surname2_sort
FROM signedup
WHERE id_Event = 78 AND status in(0,1)

UNION ALL

SELECT name, surname1, surname2, NIF, year, city, status, 'yes' as app,
       case when status = 1 then datesigned else '2099-12-31' end as datesigned_sort,
       case when status = 0 then surname1 else '' end as surname1_sort,
       case when status = 0 then surname2 else '' end as surname2_sort
FROM signedupLocal
WHERE id_Event = 78 AND status in(0,1)

ORDER BY 7 asc, 9 desc, 10 asc, 11 asc

请注意，使用UNION时，您需要使用列号，而不是ORDER BY中的列名。我使用UNION ALL因为它比UNION更有效，因为后者删除重复项 - 这会导致数据库引擎的工作。所以如果你知道没有，你可以避免这种情况。

对于排序，我使用常量来表示不应按排序列对记录进行排序的情况。

Answer 2

使用UNION个2个查询来连接结果。

SELECT * FROM (
SELECT *, "signedup" AS tablename FROM signedup WHERE …
UNION
SELECT *, "signedupLocal" AS tablename FROM signedupLocal WHERE …
) U
ORDER BY U.dateSigned DESC

带连接的Mysql查询

2 个答案: