总是选择一行sql

Question

我有一个case陈述（见下文），但我总是想要返回一个值，即使没有任何匹配WHERE类。那可能吗？谢谢

SELECT 
    CASE 
     WHEN COUNT(*) > 10 THEN 1 
     ELSE 0 
    END 
FROM 
fldt_QueryDSLAM lastDay 
WHERE AccountID = @acc 
    AND lastDay.DSL = @dsl 
GROUP BY lastDay.DSL 

Answer 1

你可以将选择包装在isnull中;

SELECT ISNULL((
    SELECT 
     CASE 
      WHEN COUNT(*) > 10 THEN 1 
      ELSE 0 
     END 
    FROM 
    fldt_QueryDSLAM lastDay 
    WHERE AccountID = @acc 
     AND lastDay.DSL = @dsl 
    GROUP BY lastDay.DSL 
), -99 /*no match*/) 

Answer 2

如果WHERE子句返回一行（或更确切地说是一个组），则删除GROUP BY。然后你会在输出中总是有一行。

我以为它会（返回一组），因为你有GROUP BY上的过滤柱和帐户ID不选择或GROOUP提及

SELECT 
    CASE 
     WHEN COUNT(*) > 10 THEN 1 
     ELSE 0 
    END 
FROM 
    fldt_QueryDSLAM lastDay 
WHERE 
    AccountID = @acc AND lastDay.DSL = @dsl 

为什么，看到这一点：Does COUNT(*) always return a result?