double vsi21=1, bi=1, bi2=1, mbi2;

SQL & ::Select(CAT_ID,S21,S22).From(CATEGORIES)
.Where(CS_ID == cid && GR_ID == gid);

Sql q_upd(::Update(CATEGORIES)(MBI, SqlArg())
.Where(CS_ID == cid && GR_ID == gid && CAT_ID == SqlArg()),
SQL.GetSession());

while(SQL.Fetch()) 
{
double vs22 = SQL[S22];
double vs21 = SQL[S21];
int k = SQL[0];

bi2 = bi*vsi21;
mbi2 = bi2*bi2*vs22*gammer*dbfactor; 
mbi2 = mbi2*mbi2; 
bi = bi2;
vsi21 = vs21;

q_upd.Run(mbi2, k);
}