sql使用sum的or的问题

[zqqazhn]

sql语句是这样的：
select sum(b1) as b1,from NB_kfq_zh where states=1 and nian=2010 and ji=1 and kfqtype='国家级开发区' or kfqtype='省级开发区'
但是我发现数据不准确，我把or后面的去掉就好使了，ji 这个是查询条件 可以是别的数字，但我查询ji=1的时候他会出现不属于ji=1的数据。这个怎么解决

[obuntu]

select sum(b1) as b1,from NB_kfq_zh where states=1 and nian=2010 and ji=1 and kfqtype='国家级开发区' or kfqtype='省级开发区'

加个括号看看

select sum(b1) as b1,from NB_kfq_zh where states=1 and nian=2010 and ji=1 and （kfqtype='国家级开发区' or kfqtype='省级开发区'）

[nightmaple]

select sum(b1) as b1,from NB_kfq_zh 
where states=1 and nian=2010 and ji=1 
and (kfqtype='国家级开发区' or kfqtype='省级开发区')

[Sharon_liu]

select sum(b1) as b1,from NB_kfq_zh where states=1 and nian=2010 and ji=1 and (kfqtype='国家级开发区' or kfqtype='省级开发区')

[永生天地]

如上，加括号