Question

此代码生成此

SELECT "End_Date"+5                                                   
                FROM exhibits e, rooms r, PlaceOfExhibition p
                WHERE "End_Date">CURRENT_DATE+5 AND r."Minimum" >= 7 and
r."Maximum" <= 16 and p."Location"=r."Name" and e."Name" = p."Exhibition" ORDER
BY "End_Date" desc;
  ?column?  
------------
 2017-01-15
 2016-12-20
 2016-10-22
 2016-09-20
(2 rows)

我需要2016-12-20日期（第二大日期），我并不总是需要第二大日期，但它取决于房间的数量是多少（如果房间查询返回4则我需要第四大一）我需要从子查询中获取此信息这是我的子查询

SELECT "End_Date"+5                                                   
                FROM exhibits e, rooms r, PlaceOfExhibition p
                WHERE "End_Date">CURRENT_DATE+5 AND r."Minimum" >= 7 and
r."Maximum" <= 16 and p."Location"=r."Name" and e."Name" = p."Exhibition" ORDER
BY "End_Date" ASC OFFSET (Select Count("Name")-1 FROM Rooms Where "Minimum">=7
and "Maximum"<=16) LIMIT 1 ;

返回此

2016-10-22

所以我的查询得到第二个最后日期，但方向错误，它是第二个最小而不是第二个

Answer 1

SELECT "End_Date"+5                                                   
                FROM exhibits e, rooms r, PlaceOfExhibition p
                WHERE "End_Date">CURRENT_DATE+5 AND r."Minimum" >= 7 and
r."Maximum" <= 16 and p."Location"=r."Name" and e."Name" = p."Exhibition" ORDER
BY "End_Date" DESC OFFSET (Select Count("Name")-1 FROM Rooms Where "Minimum">=7
and "Maximum"<=16) LIMIT 1 ;

Answer 2

您可以这样做以重新排序结果：

SELECT * FROM
(
    SELECT "End_Date"+5                                                   
    FROM exhibits e, rooms r, PlaceOfExhibition p
    WHERE "End_Date">CURRENT_DATE+5
    AND r."Minimum" >= 7
    AND r."Maximum" <= 16
    AND p."Location"=r."Name"
    AND e."Name" = p."Exhibition"
    ORDER BY "End_Date" desc
) x
ORDER BY 1 asc;

在psql中使用Asc offset和desc

2 个答案: