sql - SQL 查询：连接来自两个单独行的两个字段

Question

我有以下两个表：

USER
FID  UID     VALUE
4    3       John
3    3    Doe
4    4       Jack
3    4       Russel

应该很清楚 FID 3 = 姓氏，FID 4 = 名字。

DATEDATA
UID  DATE  
3    1234
4    4321

我想加入这两个表，所以我最终会得到这样的结果：

UID  DATE  NAME   SURNAME
3    1234  John   Doe
4    4321  Jack   Russel

或者……或者……

UID  DATE  FULLNAME
3    1234  John Doe
4    4321  Jack Russel

那里有任何 SQL 大师吗？

这是我到目前为止所拥有的：

SELECT UID, DATE, VALUE 
    from DATEDATA as D 
    left join USER as U 
    on U.uid = D.uid where fid = 3 OR fid = 4

但这给了我这个：

UID  DATE  VALUE
3    1234  Doe
3    1234  John
4    4321  Russel
4    4321  Jack

任何人？

Answer 1

SELECT D.UID, DATE, U.VALUE + ' ' + U2.Value as fullName
from DATEDATA as D 
left join USER as U on U.uid = D.uid and U.fid = 3
left join USER as U2 on U2.uid = D.uid and U2.fid = 4

尽管只要 first 或 last 为 NULL，这可能会给您一个 NULL 名称。在这种情况下，如果您可以接受用户在您的系统中只有一个名称或另一个名称的情况，您可能希望使用 ISNULL 将任一名称设为空字符串。

Answer 2

SELECT A.UID, DATEDATA.DATE, A.VALUE, B.VALUE from DATEDATA, USER A, USER B 
WHERE A.UID = B.UID AND A.FID = 3 AND B.FID = 4 AND DATEDATA.UID = A.UID

Answer 3

select 
  D.UID
, D.DATE
, isnull(U.VALUE, '') 'firstName'
, isnull(U2.VALUE, '') 'surName'
from
  DateData D
left join User U on U.uid = D.uid and U.fid = 3
left join User U2 on U2.uid = D.uid and U2.fid = 4

Answer 4

您可以使用以下内容。它假定您总是有名字。如果您总是有一些字段并且它不是名字，请将其设为第一个并重新调整连接。如果您永远无法保证价值，请告诉我们，我们会努力提供解决方案。

select d.uid,COALESCE(d.date,'none entered'),COALESCE(frst.value,'') as NAME,COALESCE(lst.value,'') as SURNAME
from
user frst (NOLOCK)
left join user lst (NOLOCK) on lst.uid=frst.uid
left join datedata d (NOLOCK) on d.uid = frst.uid
where
frst.fid=4
AND lst.fid=3