为 SQL case 表达式中的“Then”子句返回多个值

Question

My "files" table data is

fileid   file1      file2
  1      abc.pdf    abcde.pdf
  2      ghf.pdf    ghfjkl.pdf
  3      hjy.pdf    hjyui.pdf

my "sampletable" data is

 fileid       names
   1           abc
   2           ghf
   3           hjy
   4           juk

I need output like

   fileid      names    files

     1          abc      abc.pdf
     1          abc      abcde.pdf
     2          ghf      ghf.pdf
     2          ghf      ghfjkl.pdf
     3          hjy      hjy.pdf
     3          hjy      hjyui.pdf

i tried the following query but not getting desired output

 select st.fileid,st.contolnames,
 case when st.fileid in (select fileid from Files) 
 then f.file1 
 when st.fileid in (select fileid from Files)  then f.file2 end as Files
 from sampletable st
 join Files f on f.fileid=st.fileid 

Please help with this demo: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=08337e2ee351b573bc902f06fcfba272

Answer 1

You can try below - use UNION

DEMO

    select * from
    (
    select a.fileid,contolnames,file1 as files
    from Files a inner join sampletable b on a.fileid=b.fileid
    union
    select a.fileid,contolnames,file2 as files 
    from Files a inner join sampletable b on  a.fileid=b.fileid
  )A order by fileid

OUTPUT:

fileid  contolnames files
1         abc   abc.pdf
1         abc   abcdef.pdf
2         ghf   ghf.pdf
2         ghf   ghfjkl.pdf
3         hjy   hjyui.pdf
3         hjy   hjy.pdf

Answer 2

To generate two rows for each record you can use CROSS JOIN like following query to get the desired output.

select f.fileid, 
       st.contolnames as names, 
       case 
         when t.x = 1 then f.file1 
         else file2 
       end            as files 
from   Files f 
       inner join sampletable st 
               on st.fileid = f.fileid 
       cross join (select 1 x 
                   union 
                   select 2 x) t(x) 
order  by fileid 

Online Demo

Answer 3

Try this one. it's working for me..

CREATE TABLE #Temp1(fileid INT IDENTITY, file1 varchar(50), file2 varchar(50))
CREATE TABLE #Temp2(fileid INT IDENTITY, name varchar(50))
CREATE TABLE  #Temp3(fieldid int, name varchar(50), file1 varchar(50) , file2 varchar(50))
create table #Temp4 (fieldid int, name varchar(50), files varchar(50))  

INSERT INTO #Temp1 VALUES( 'abc.pdf','abcde.pdf')
INSERT INTO #Temp1 VALUES( 'ghf.pdf','ghfjkl.pdf')
INSERT INTO #Temp1 VALUES( 'hjy.pdf','hjyui.pdf')


INSERT INTO #Temp2 VALUES( 'abc')
INSERT INTO #Temp2 VALUES( 'ghf')
INSERT INTO #Temp2 VALUES( 'hjy')
INSERT INTO #Temp2 VALUES( 'juk')

SELECT * FROM #Temp1
SELECT * FROM #Temp2


INSERT INTO #Temp3
SELECT * FROM (SELECT B.fileid ,name , 
CASE WHEN Name Like SUBSTRING(A.file1,1,3) THEN file1  END AS files, 
CASE WHEN Name Like SUBSTRING(A.file2,1,3) THEN  file2 END AS files1   
FROM #Temp1 A , #Temp2 B ) AA WHERE files IS NOT NULL

INSERT INTO #Temp4 SELECT fieldid,name,file1 FROM  #Temp3 

INSERT INTO #Temp4 SELECT fieldid,name,file2 FROM  #Temp3 

SELECT * FROM #Temp4 ORDER BY name asc

DROP TABLE #Temp1
DROP TABLE #Temp2
DROP TABLE #Temp3
DROP TABLE #Temp4

Answer 4

Just make a join with the UNPIVOT of the first Table.

select f.fileid, name, files 
from Files f 
unpivot (files for name in (file1,file2)) 
join sampletable s on f.fileid = s.fileid