更新语句的思考错误

Question

运行此更新语句后

update lol as l 
set prodnr = p.prodnr
from prog as p
where  (l.ponr in ('1000') and  l.abo=p.abo and l.sto=p.sto and l.ponr=p.ponr 
and l.prodnr!=p.prodnr)

我希望以下select语句产生0条记录

select *
from lol l, prog p  
where (l.ponr in ('1000') and  l.abo=p.abo and l.sto=p.sto and l.ponr=p.ponr 
and l.prodnr!=p.prodnr)

但不幸的是，情况并非如此...... 为什么？

修改 我几乎疯了......我想，问题是，表条件中有多条记录用于这种情况：l.abo = p.abo和l.sto = p.sto和l.ponr = p.ponr 和l.prodnr！= p.prodnr。在我添加以下附加条件后：

and p.pversion notnull and p.pversion !='0' and p.pversion = l.pversion 

所以表达式如下：

update lol as l 
set prodnr = p.prodnr
from prog as p
where  (l.ponr in ('1000') and  l.abo=p.abo and l.sto=p.sto and l.ponr=p.ponr 
and l.prodnr!=p.prodnr and p.pversion notnull and p.pversion !='0' and p.pversion = l.pversion)

选择

select *
from lol l, prog p  
where (l.ponr in ('1000') and  l.abo=p.abo and l.sto=p.sto and l.ponr=p.ponr 
and l.prodnr!=p.prodnr and p.pversion notnull and p.pversion !='0' and p.pversion = l.pversion)

产生0条记录。所以我想知道，如果第一次更新真的更新任何东西。也许是第一个创建的记录，它符合条件＆＃39;（l.ponr in（＆＃39; 1000＆＃39;）和l.abo = p.abo和l.sto = p.sto和l.ponr = p.ponr 和l.prodnr！= p.prodnr）＆＃39;