Get header as the first row in dynamic SQL - sql

Question

My table:
id name city
--------------------
1 Jim NewYork
2 Rose London
3 Kitty Seattle
......
The output:
id name city
--------------------
id name city
1 Jim NewYork
2 Rose London
3 Kitty Seattle
I can easily do it in static SQL like this, but how to do it in dynamic SQL?
Declare #sql as varchar(max)='select *';
set #sql =#sql+' from mytable';
exec(#sql)

Answer 1

I am not sure why you want to do that as your id looks int to me. If you want one extra string type value to the column to appear on the top, in that case you have to convert all the int to string.
Still if you want to do that you can write your query like following.
SELECT *
FROM (
SELECT cast(id AS VARCHAR(10)) AS id
,Name
,city
FROM mytable
UNION ALL
SELECT 'id'
,'name'
,'city'
) t
ORDER BY CASE
WHEN t.id = 'id'
THEN 0
ELSE 1
END
Same query can be written as dynamic query like following.
DECLARE #sql AS VARCHAR(max) = 'select * from (
select cast(id as varchar(10)) as id,Name,city';
SET #sql = #sql + ' from mytable union select ''id'',''name'', ''city'')t
order by case when t.id=''id'' then 0 else 1 end';
EXEC (#sql)

Answer 2

I don't know if I am overdoing this. But if you want a pure dynamic way, you can try something like
declare #sql varchar(max),
#colnameHeads varchar(max),
#colnames varchar(max);
-- building the row with column headers
set #colnameHeads = STUFF((
SELECT ',''' + COLUMN_NAME + ''''
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = N'<your-table>'
FOR XML PATH('')
), 1, 1, '')
-- casting all the values to varchar to match with header row
set #colnames = STUFF((
SELECT ',' + CONCAT('CAST(', COLUMN_NAME, ' AS VARCHAR(100))')
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = N'<your-table>'
FOR XML PATH('')
), 1, 1, '')
-- dynamic script
set #sql = 'select '+ #colnameHeads + ' union all select '+ #colnames + ' from <your-table>';
EXEC (#sql)