fromtable : NAME
                 | aliasx
                 | '(' selectx ')' kw_as NAME

def p_fromtable(self,t):
    """fromtable : NAME
                 | aliasx
                 | '(' selectx ')' kw_as NAME
    """
    if len(t)==6: t[0]=AliasX(t[2],t[5])
    elif len(t)==2: t[0]=t[1]
    else: raise NotImplementedError('unk_len',len(t)) # pragma: no cover