postgis - How to achieve equivalent to Dissolve from ArcGIS for Desktop using ST_Union?

I am trying to achieve an equivalent to the Dissolve tool from ArcGIS for Desktop using ST_Union from PostGIS but it seems I am not getting expected result.

I have one table which has certain attributes with the Polygon Geometry. (like FID, Locstat, Loccnt, Shape)

Here is my query :

SELECT c.fid, ST_Union(c.boundaryshape) FROM c Group by c.fid,c.boundaryshape;