在另一个SQL查询中使用一个查询的结果

Question

I have below table structure :

Table1

╔═════╦══════╦═════════════╦═════════════╗
║Col1 ║ Col2 ║ TableName   ║ ColumnName  ║
╠═════╬══════╬═════════════╬═════════════╣
║  1  ║ abc  ║ Table2      ║ column2     ║
║  2  ║ xyz  ║             ║             ║
║  3  ║ pqr  ║ Table1      ║ column1     ║
║  4  ║ jbn  ║             ║             ║
╚═════╩════════════════════╩═════════════╝

Table2 :   

 ╔════════╦═════════╗
 ║Column1 ║ Column2 ║
 ╠════════╬═════════╣
 ║  1     ║ A       ║
 ║  2     ║ B       ║
 ║  3     ║ C       ║
 ║  4     ║ D       ║
 ╚════════╩═════════╝

Table3

╔════════╦═════════╗
║Column1 ║ Column2 ║
╠════════╬═════════╣
║  1     ║ X       ║
║  2     ║ Y       ║
║  3     ║ Z       ║
║  4     ║ A       ║
╚════════╩═════════╝

I want to write stored procedure which will select data from Table1 and data from another table depending upon value of column tableName and columnName in Table1.

I want data in following format:

╔═════╦═════╦════════╗
║Col1 ║ Col2║ List   ║
╠═════╬═════╬════════╣
║  1  ║ abc ║A,B,C,D ║
║  2  ║ xyz ║        ║
║  3  ║ pqr ║1,2,3,4 ║
║  4  ║ jbn ║        ║
╚═════╩═════╩════════╝

Answer 1

Try temporary table . look at here : http://www.sqlteam.com/article/temporary-tables

Answer 2

You will need a dynamic sql to get such a select. Check out the link http://www.mssqltips.com/sqlservertip/1160/execute-dynamic-sql-commands-in-sql-server/

EDIT:

The following code should do the trick.

I have assumed that the column Col1 in Table1 is of type int.

I have used Temp table to generate the required table. You can replace it will your table as per your convenience. Also I have used #table1 which you can replace with your Table1 .

Also this might not be very good in terms of performance but this is the best I could come up with right now.

declare @count int, @Query VARCHAR(5000), @counter int, @tableName VARCHAR(50), @ColumnName VARCHAR(50), @Col1 INT, @Col2 VARCHAR(50)
select @count = count(0) from #table1
SET @counter = 1

CREATE TABLE #table4
(
    Col1 INT,
    Col2 VARCHAR(50),
    List VARCHAR(50)
)

WHILE @counter <= @count
BEGIN
    SELECT @tableName = TableName, @ColumnName = columnName, @Col1 = Col1, @Col2 = Col2 FROM #Table1 WHERE Col1 = @counter

    SELECT @Query = 'INSERT INTO #table4 (Col1 , Col2) VALUES (' + CONVERT(varchar(50),@Col1) + ', ''' + @Col2 + ''')'
    EXEC (@Query)
    SELECT @Query = ''

    IF ISNULL(@tableName, '') != '' AND ISNULL(@ColumnName, '') != ''
    BEGIN
        SELECT @Query = 'UPDATE #table4 SET LIST = STUFF((SELECT '','' + CONVERT(VARCHAR(50), ' + @ColumnName + ') FROM ' + @tableName + ' FOR XML PATH('''')),1,1,'''') WHERE Col1 = ' + CONVERT(varchar(50),@Col1)

        EXEC (@Query)
    END
    SET @counter = @counter + 1
END

SELECT * FROM #table4

Hope this helps

Answer 3

Answer edited for incorporating n no of rows

CODE

 drop table #temp1
declare @tabletemp as varchar (10)
declare @columntemp as varchar (10)
Declare @sqlTemp NVARCHAR(400)
declare @counter1 as int
declare @counter2 as int
select @counter2 = 1

select name,cname into #temp1 from test1
select @counter1 = COUNT(*) from #temp1


while (@counter2<= @counter1)
begin
SET @tabletemp = (SELECT MIN(name) FROM #temp1)
select @columntemp = (select min(cname) from #temp1 where #temp1.name = @tabletemp)

set @sqlTemp='select '+@columntemp +'  from '+@tabletemp
exec(@sqlTemp)

delete from #temp1 where name = @tabletemp and cname = @columntemp

select @counter1 = COUNT(*) from #temp1
end

RESULT

select * from test1 
name    cname
table1  column1
test2   colname
table1  test
test2   name

---

select column1 from table1
column1
qwer
asdff
zxcvb
qwer
asdff
zxcvb

---

select colname from test2
colname
testing
wer
ewrth
sfsf
testing
wer
ewrth
sfsf

---

select test from table1
--got error message inavlid column nae 'test' as this column does not exist

---

select name from test2 
name
table1
table1
table3
table2
table1
table1
table3
table2