sql语句没看懂 请先森们 给我一臂之力！

string sql = "select EXPORT_GOODS_ID,GOODS_NAME,GOODS_STANDARD,EXPORT_PACK_QUANTITY"
+"EXPORT_PLAN_QUANTITY,EXPORT_WEIGHT,EXPORT_GOODS_TYPE"
+"EXPORT_GOODS_STATUS,EXPORT_LOT_NO,EXPORT_BATCH_NO,EXPORT_ONLINE_STATUS"
+ "GOODS_BAR,EXPORT_REMARK "
+ "from Wms_Export_Notifydetail "
+ "left join wms_base_goods on GOODS_ID=EXPORT_GOODS_ID "
+ "where Export_ID='" + id + "' and Export_list_no='" + list_no + "'";
中的 + "from Wms_Export_Notifydetail "
+ "left join wms_base_goods on GOODS_ID=EXPORT_GOODS_ID "
+ "where Export_ID='" + id + "' and Export_list_no='" + list_no + "'";怎么解释
left.......on....是什么意思

• "from Wms_Export_Notifydetail "
  • "left join wms_base_goods on GOODS_ID=EXPORT_GOODS_ID "
  • "where Export_ID='" + id + "' and Export_list_no='" + list_no + "'"; Wms_Export_Notifydetail表名 wms_base_goods 表名 想把两个表连接起来按GOODS_ID=EXPORT_GOODS_ID这个条件连接。合成一个大表、

left join 表示 左外联； on 表示关联的字段条件