一个关于in关键字的奇怪的SQL语句

select SubContractPartID,sum(CostCheckDSumMoney) SumMoney from TX_Project_SubContractPartRationMonth
 where SubContractPartID in (select SubContractPartID from TX_Project_SubContractPart where ProjectID=10044 and StatYear='2007' and StatMonth='12')
group by SubContractPartID

select SubContractPartID,sum(CostCheckDSumMoney) SumMoney from TX_Project_SubContractPartRationMonth
 where SubContractPartID in (select SubContractPartID from TX_Project_SubContractPart where ProjectID=10044) and StatYear='2007' and StatMonth='12'
group by SubContractPartID

 

两个sql语句执行效果竟然一样，而TX_Project_SubContractPart表没有StatYear、StatMonth这两个字段