mysql-下面两个查询语句有什么区别

SELECT A.YWSJMS1 as ywsjms1 ,A.YWSJMS1 as ywsjms2,A.YWSJ1 as ywsj1,A.cjsj as cjsj,B.DDLB as ddlb from GY_XT_CZJL A, SW_DD_JL B  where A.SCBJ= 0 AND B.SCBJ=0 AND A.YWSN=B.SNSELECT A.YWSJMS1 as ywsjms1 ,A.YWSJMS1 as ywsjms2,A.YWSJ1 as ywsj1,A.cjsj as cjsj,B.DDLB as ddlb from GY_XT_CZJL A  LEFT JOIN SW_DD_JL B   ON A.SCBJ= 0 AND B.SCBJ=0 AND A.YWSN=B.SN