0

データベース名に「train delay, with columns」というテーブルがあります

train number(int),
DelayTime(int),
DelayReason(nchar)

そのため、列車には遅延理由ごとに複数の遅延時間がある場合があります。次に例を示します。

trainnumber,Delaytime,DelayReason
1          ,5 sec    ,x
1          ,10 sec    ,Z
1          ,70 sec    ,TY

次のデザインの Crystal レポートを作成したいと考えています。

trainnumber, delaytime 1,delay reason 1 ,delaytime 2, delay reason 2,delaytime 3,delay reason 3

しかし、この結果を得るクエリがわかりません。

私はこれを試しました：

select delaytime from dbo.traindelay

しかし、出力は次のようになります。

Delaytime
5
10
70

そして、私はそれを望んでいません。私はこのようなものが欲しい：

delaytime1 ,delaytime2 ,delaytime3
4

1 に答える 1

0

First, I'll propose a new structure by adding a column called Id so now you have 2 tables :

  • Train(int Id, string Name)
  • TrainDelay (int Id, int TrainId, int DelayTime, nchar DelayReason

The SQL Query to have a maximum of 3 delays per train is :

select 
  t.Name, 
  d1.DelayTime   as Delay1, 
  d1.DelayReason as Reason1,
  d2.DelayTime   as Delay2, 
  d2.DelayReason as Reason2,
  d3.DelayTime   as Delay3, 
  d3.DelayReason as Reason3,
from Train as t
left join TrainDelay as d1 on d1.TrainId = t.Id 
left join TrainDelay as d2 on d2.TrainId = t.Id and d2.Id > d1.Id
left join TrainDelay as d3 on d3.TrainId = t.Id and d3.Id > d2.Id

Note that if you have more than 3 delays for the same train, then you would have multiple results per train with duplicated records. You can add more joins but it would get extremelly slow if your table is big.

于 2009-11-02T16:55:42.557 に答える