Question

我正在尝试找出SQL来汇总我的Vehicles表中的数据：

Id | Name  | Make
---+-------+------
1    Car      Ford
1    Car      Volvo
1    Car      BMW
2    Bike     Honda
3    Truck    Tata
3    Truck    abc
4    Train    bullet

以返回以下内容：

Id | Name  | Result
---+-------+------
1    Car      3 items selected
2    Bike     Honda
3    Truck    2 items selected
4    Train    bullet

因此，如果Id,Name组合具有多个制造商，则输出“ X个选定项目”，其中X是该组合的制造商数量。否则，按原样输出Make。请注意，对于每个Id，Name组合而言，make都是唯一的。

这可以使用GROUP BY表达式实现吗？如果是这样，我需要什么聚合函数来代替???？下面？还是可以通过其他方式实现？

select Id, 
    Name, 
    case when count(Make) > 1 then convert(varchar(10), count(Make)) + ' items selected'
    else ??? end Result
from Vehicles 
group by Id, Name

我正在使用SQL Server 2008。

Answer 1

使用<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.4/jquery.min.js"></script> <div class="form-row"> <div class="col-md-12"> <div class="form-group"> <label id="ratestructureLabel">Required Rate Structure:</label> <br/> <div class="form-check"> <input class="form-check-input" type="radio" name="ratestructure" id="allin" value="all-in"> <label class="form-check-label" for="yesebiz">All-In</label> </div> <div class="form-check"> <input class="form-check-input" type="radio" name="ratestructure" id="allindest" value="all-inD"> <label class="form-check-label" for="allindest">All-In, subject to Destinations</label> </div> <div class="form-check"> <input class="form-check-input" type="radio" name="ratestructure" id="allinori" value="all-inO"> <label class="form-check-label" for="allinori">All-In, subject to Origins</label> </div> <div class="form-check"> <input class="form-check-input" type="radio" name="ratestructure" id="boforindest" value="bofOD"> <label class="form-check-label" for="boforindest">BOF, subject to Origins & Destination</label> </div> <div class="form-check"> <input class="form-check-input" type="radio" name="ratestructure" id="pernote2" value="pernote2"> <label class="form-check-label" for="pernote2">Per Note 2</label> </div> <div class="form-check"> <input class="form-check-input" type="radio" name="ratestructure" id="surcharges" value="surcharges"> <label class="form-check-label" for="surcharges">Surcharges per tariff</label> </div> <div class="form-check form-check-inline otherrate"> <input class="form-check-input" type="radio" name="ratestructure" id="otherrate" value="Other Rate"> <label class="form-check-label" for="otherrate">Other:</label> <input type="text" class="form-control ml-2" name="otherstructure" id="otherrateIn" placeholder=""> </div> </div> </div> </div> <button id="nextsales3Btn">Check</button>或MIN()：

MAX()

如果只有一行，则select Id, Name, (case when count(Make) > 1 then convert(varchar(10), count(Make)) + ' items selected' else min(Make) end) as Result from Vehicles group by Id, Name;和MIN()是该行的值。

Answer 2

使用CTE（公用表表达式），因为这样可以提高查询性能，尤其是在查询中。检查查询

      WITH Vehicles_CTE (Id, Name, Result,Make) 
      AS (  
          SELECT Id, Name, COUNT(1) Result, MAX(Make) Make   FROM   Vehicles
          Group By Id, Name 
         ) 
         SELECT Id, Name, CASE WHEN Result>1 
                            THEN Cast(Result AS varchar(10)) + ' items selected' 
                            ELSE Make End  Result FROM   Vehicles_CTE

SQL按汇总varchar列分组

2 个答案: