Question

我想检查条件内的查询

如果查询为空，我想要值'NO'，如果查询不为空，我想要值'YES'

通过尝试，如果条件出现错误。

我的查询是

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')

我尝试了

IF(above query is NULL) THEN 'NO'
ELSE 'YES'
END IF

稍后我需要在select语句中

Select ContractID, ContractName, IF(above query is NULL) THEN 'NO'
ELSE 'YES' AS Status FROM Contract

我该怎么做？

Answer 1

在 mysql 中，您可以使用 exist

喜欢

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，类似

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 ;

Answer 2

Select ContractID, ContractName,  case when SiteCount > 0 then 'YES' ELSE 'NO' END as Status
FROM Contract c
left join (
    SELECT ContractNumber, Count(SiteID) as SiteCount
    from ChartFace 
    Inner Join Structure on Structure.StructureID = ChartFace.StructureID
    where (ContractNumber='C197960' AND LineNumber=4) 
      AND (ISNULL('MN420628', '-1')='-1' or SiteID = 'MN420628')
    group by ContractNumber
  )  tbl on c.ContractNumber = tbl.ContractNumber

Answer 3

我相信CASE是您的追求。

SELECT ContractID, ContractName,
 CASE
  WHEN COUNT(SiteID) IS 0 THEN 'NO'
  ELSE 'YES'
 END AS HasSite
FROM ChartFace
 INNER JOIN Structure on Structure.StructureID = ChartFace.StructureID
 WHERE ContractNumber='C197960' AND LineNumber=4
 AND (ISNULL('MN420628', '-1')='-1' or SiteID = 'MN420628')

这将返回以下内容：

{ ContractID:  3, ContractName: 'REALLY IMPORTANT CONTRACT', HasSite: 'NO' }

Answer 4

COUNT(*)永远不能为null。您可以将其与零进行比较：

select
  contractid,
  contractname, 
  case when
    (
      select count(*)
      from chartface cf
      join structure s on s.structureid = cf.structureid
      where cf.contractnumber = c.contractid
      and ...
    ) = 0 then 'NO' else 'YES' end as status
from contract c
order by contractid;

但是，如果您只想检查是否存在，为什么要数一数呢？为此，我们在SQL中使用EXISTS或IN：

select
  contractid,
  contractname, 
  case when contractid in
    (
      select cf.contractnumber
      from chartface cf
      join structure s on s.structureid = cf.structureid
      where  ...
    ) then 'YES' else 'NO' end as status
from contract
order by contractid;

如何在IF条件下检查查询是否为空？

4 个答案: