如何检查查询是否为 IF 条件内为空？

在mysql中，您可以使用exist，就像

SELECT  ContractID, ContractName,IF( EXISTS(
SELECT 
    Count(SiteID)
FROM ChartFace 
    INNER JOIN Structure ON Structure.StructureID = ChartFace.StructureID
WHERE (ContractNumber='C197960' AND LineNumber=4) AND 
    (ISNULL('MN420628', '-1')='-1' or SiteID = 'MN420628')),'yes','No') Status 
FROM Contract ;

在SQL Server中：

SELECT ContractID, ContractName,CASE
     WHEN EXISTS (SELECT 
    Count(SiteID)
FROM ChartFace 
    INNER JOIN Structure ON Structure.StructureID = ChartFace.StructureID
WHERE (ContractNumber='C197960' AND LineNumber=4) AND 
    (ISNULL('MN420628', '-1')='-1' or SiteID = 'MN420628')) THEN 'yes'
     ELSE 'NO'
   END as  Status 
FROM Contract ;