sql - columns to rows maintaining userid -

i have columns this:

userid    col1    col2    col3    col4 --------------------------------------- 233432    45.2    34.2    ''      0.52 

i want this:

userid    colid    value ------------------------- 233432    col1     45.2 233432    col2     34.2 233432    col3     '' 233432    col4     0.52 

i found link below:

column row in sql server?

but doesn't answer question have.my question. using sql server 2012.

select userid,'col1',col1 'value' mytable union select userid,'col2',col2 mytable union select userid,'col3',col3 mytable union select userid,'col4',col4 mytable