SQL Server : dynamically select column based on another select column - sql-server

Question

I would like to write a query that returns two columns. The first column would be all of the column names of an existing table (ImportTable) sorted alphabetically, and the second column would be a sample row from that table (ImportTable) showing a potential value for one of those columns.
This is the pseudo code I have so far:
select
c.name as 'Column Name',
(select top(1) ImportTable."c.name"
from Database.dbo.[ImportTable] ImportTable) as 'Sample Column Value'
from
Database.sys.columns c
inner join
Database.sys.objects o on o.object_id = c.object_id
where
o.name = 'ImportTable'
order by
c.name asc
I don't know how to dynamically select the column ImportTable."c.name" based on the value of the column name. I'm not even sure what to search for that.

Answer 1

You need to create a dynamic unpivot statement and execute it.
Try not to get confused about what is the static and what the dynamic parts.
DECLARE #sql nvarchar(max) = N'
SELECT v.*
FROM (
SELECT TOP (1) *
FROM ' + QUOTENAME(#tablename) + N'
ORDER BY CHECKSUM(NEWID())
) t
CROSS APPLY (VALUES
' +
(
SELECT STRING_AGG(CAST(
N'(' + QUOTENAME(c.name, '''') + N', CAST(t.' + QUOTENAME(c.name) + N' AS sql_variant))'
AS nvarchar(max)), N',
') WITHIN GROUP (ORDER BY c.name ASC)
FROM sys.columns c
WHERE c.object_id = OBJECT_ID(#tablename)
) +
N'
) AS v(columnName, columnValue);
';
PRINT #sql; -- for testing
EXEC sp_executesql #sql;
If you are unfortunate enough to still be on a version not supporting STRING_AGG, you can use FOR XML instead for that part:
-------
CROSS APPLY (VALUES
' +
STUFF(
(
SELECT N',
(' + QUOTENAME(c.name, '''') + N', CAST(t.' + QUOTENAME(c.name) + N' AS sql_variant))'
FROM sys.columns c
WHERE c.object_id = OBJECT_ID(#tablename)
ORDER BY c.name ASC
FOR XML PATH(''), TYPE
).value('text()[1]', 'nvarchar(max)'), 1, 2, '') +
N'
) AS v(columnName, columnValue);
';
--------

Answer 2

With a little dynamic SQL, you can get this done with just a series of UNION selects. This doesn't require string_agg or any recent SQL feature.
declare #table sysname = N'schema.YourTableName';
-- Begin with a CTE to select 1 row at random:
declare #stmt nvarchar(max) = N'with cte as (select top(1)* from ' + #table + ' order by newid())';
-- Create string of UNION selects:
select #stmt = #stmt
+ 'select '''
+ name
+ ''' as ColumnName, cast('
+ name
+ ' as varchar(max)) as SampleValue from cte union '
from sys.columns
where object_id = object_id(#table)
-- Remove the trailing "union"
set #stmt = left(#stmt,len(#stmt)-5);
-- Add the ORDER
set #stmt = #stmt + ' order by ColumnName';
-- Execute the query:
exec sp_executesql #stmt = #stmt;