Using a parameter in Group by clause gives error "GROUP BY expression must contain at least one column that is not an outer reference"

Suppose you have a table 'tblTest' with column named 'Col1', 'Col2'.

And you have a parameter 

Declare @param nvarchar(50)

Suppose you want to group by column with parameter.

Select @param as Parameter, Col1, Col2 , Count (Col1) from tblTest

group by @param, Col1, Col2

Above query will give error:

Using a parameter in Group by clause gives error "GROUP BY expression must contain at least one column that is not an outer reference"

Solution : You just remove @param from group by clause.

Select @param as Parameter, Col1, Col2 , Count (Col1) from tblTest

group by  Col1, Col2