mysql 大神们帮我看看对着吗 左连接 右连接 全连接

1##连接Store_Information 表格与Geography 表格，实现各区域各店铺销售情况，左表全显示，右表只显示store_name在左表出现的记录（region_name ,store_name,Sales )
select A1.region_name region_name,A1.store_name,sum(A2.Sales) Sales from geography A1 left join store_information A2 on A1.store_name = A2.store_name group by A1.region_name,A1.store_name;

2##连接Store_Information 表格与Geography 表格，实现各区域各店铺销售情况，右表全显示，左表只显示store_name在右表出现的记录（region_name ,store_name,Sales )
select A1.region_name region_name,A1.store_name,sum(A2.Sales) Sales from geography A1 right outer join store_information A2 on A1.store_name = A2.store_name group by A1.region_name,A1.store_name;

3##连接Store_Information 表格与Geography 表格，实现各区域各店铺销售情况，右表左表均全显示（region_name ,store_name,Sales )
select A1.region_name region_name,A1.store_name,sum(A2.Sales) Sales from geography A1 left join store_information A2 on A1.store_name = A2.store_name union select A1.region_name region_name,A1.store_name,sum(A2.Sales) Sales from geography A1 right outer join store_information A2 on A1.store_name = A2.store_name group by A1.region_name,A1.store_name;