i have a string with my needed columns, which i want to select. For example:
@sqlstring = 'col1,col2,col3'
I want select columns from table using this string. Like
SELECT @sqlstring FROM MyTable
But choose only this string, as much as columns count in table
col1,col2,col3
col1,col2,col3
col1,col2,col3
You need to use dynamic SQL. When doing so in SQL Server, I recommend using sp_executesql:
declare @sql varchar(max);
set @sql = '
select @sqlstring
from my_table
';
set @sql = replace(@sql, '@sqlstring', @sqlstring);
exec sp_executesql @sql;
In SQL Server 2016 they have introduced Split string function: STRING_SPLIT
DECLARE @sqlstring varchar(100) = 'col1,col2,col3'
DECLARE @Delimiter CHAR = ','
SELECT LTRIM(RTRIM(Split.a.value('.', 'VARCHAR(100)'))) 'Value'
FROM
(
SELECT CAST ('<M>' + REPLACE(@sqlstring, @Delimiter, '</M><M>') + '</M>' AS XML) AS Data
) AS A
CROSS APPLY Data.nodes ('/M') AS Split(a)
