added test of len() method for SQLTable
added test of len() method for SQLTable

cjlee112/pygr,theoryno3/pygr,theoryno3/pygr,RitwikGupta/pygr,theoryno3/pygr,GenDataPro/pygr,GenDataPro/pygr,RitwikGupta/pygr,cjlee112/pygr,GenDataPro/pygr,cjlee112/pygr,RitwikGupta/pygr,cjlee112/pygr