select *
LEFT JOIN 订单明细 x ON ( d."订单ID" = x."订单ID" )
LEFT JOIN 产品 c ON ( x."产品ID" = c."产品ID" )
LEFT JOIN 产品类别 b ON ( c."类别ID" = b."类别ID" )
SELECT * FROM (
select 货主地区,产品名称,数量,row_number() over(partition by 货主地区 ORDER BY 数量 DESC) RN from (
select 货主地区,产品名称,sum(数量) 数量 from (
select * from 订单 d
LEFT JOIN 订单明细 x ON d."订单ID" = x."订单ID"
LEFT JOIN 产品 c ON x."产品ID" = c."产品ID"
LEFT JOIN 产品类别 b ON c."类别ID" = b."类别ID"
) group by 货主地区,产品名称
)
WHERE RN=1