请教一个问题大数据计算MaxCompute不删掉返回120W条，请问这是为什么？

请教一个问题大数据计算MaxCompute
with t1 as (
select guid from xag_datacenter.dwd_log_eve_farmService_LandInfo_d_day
where pt>=20230101 and nvl(guid,'')!='' group by guid
),
t2 as (
select guid from XAG_DataCenter.dwd_task_public_land_d_day
where pt>=20230101 and pt<=20230731 and create_source=1 and nvl(guid,'')!=''
and guid not in (select guid from t1) group by guid
)select * from t2;
这段代码，删掉nvl(guid,'')!=''返回0条，不删掉返回120W条，请问这是为什么？