IF NOT EXISTS(
    SELECT * FROM sys.columns 
    WHERE Object_ID = Object_ID(N'pal_Surface') AND Name = N'isComparable')
BEGIN
    ALTER TABLE pal_Surface ADD isComparable BIT
END

IF NOT EXISTS(
    SELECT * FROM sys.columns 
    WHERE Object_ID = Object_ID(N'pal_SurfaceField') AND Name = N'isComparable')
BEGIN
    ALTER TABLE pal_SurfaceField ADD isComparable BIT CONSTRAINT [DF_pal_SurfaceField_isComparable] DEFAULT ((0)) NULL;
END