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看一条sql
select q.*, r.goods_name from (select nvl(t.goods_code, s.goods_code) goods_code, t.buy_open_price, t.buy_position_price, t.buy_position_amount, s.sale_open_price, s.sale_position_price, s.sale_position_amount, (nvl(t.buy_position_amount, 0) - nvl(s.sale_position_amount, 0)) position_amount from (select opo.goods_code, opo.position_bs, sum(opo.open_price * opo.position_amount) / sum(opo.position_amount) buy_open_price, sum(opo.position_price * opo.position_amount) / sum(opo.position_amount) buy_position_price, sum(opo.position_amount) buy_position_amount from otc_trade_position_open opo where opo.position_bs = ‘1‘ and opo.account_type = ‘1‘ and position_bs = ‘2‘ group by opo.goods_code, opo.position_bs) t full outer join (select opo.goods_code, opo.position_bs, sum(opo.open_price * opo.position_amount) / sum(opo.position_amount) sale_open_price, sum(opo.position_price * opo.position_amount) / sum(opo.position_amount) sale_position_price, sum(opo.position_amount) sale_position_amount from otc_trade_position_open opo where opo.position_bs = ‘2‘ and opo.account_type = ‘1‘ and position_bs = ‘2‘ group by opo.goods_code, opo.position_bs) s on (t.goods_code = s.goods_code)) q left outer join otc_goods r on (q.goods_code = r.goods_code)
结果如下
再看下一个sql
select q.*, r.goods_name from (select nvl(t.goods_code, s.goods_code) goods_code, t.buy_open_price, t.buy_position_price, t.buy_position_amount, s.sale_open_price, s.sale_position_price, s.sale_position_amount, (nvl(t.buy_position_amount, 0) - nvl(s.sale_position_amount, 0)) position_amount from (select opo.goods_code, opo.position_bs, sum(opo.open_price * opo.position_amount) / sum(opo.position_amount) buy_open_price, sum(opo.position_price * opo.position_amount) / sum(opo.position_amount) buy_position_price, sum(opo.position_amount) buy_position_amount from otc_trade_position_open opo where opo.position_bs = ‘1‘ and opo.account_type = ‘1‘ and position_bs = ‘1‘ group by opo.goods_code, opo.position_bs) t full outer join (select opo.goods_code, opo.position_bs, sum(opo.open_price * opo.position_amount) / sum(opo.position_amount) sale_open_price, sum(opo.position_price * opo.position_amount) / sum(opo.position_amount) sale_position_price, sum(opo.position_amount) sale_position_amount from otc_trade_position_open opo where opo.position_bs = ‘2‘ and opo.account_type = ‘1‘ and position_bs = ‘1‘ group by opo.goods_code, opo.position_bs) s on (t.goods_code = s.goods_code)) q left outer join otc_goods r on (q.goods_code = r.goods_code)
查询方法一样，就是条件变了一下，可是联合查询的商品名称却在上面一个里面查询不出来，而下面一个里面显示正常。分析原因，nvl函数的问题，nvl(t.goods_code, s.goods_code) 前面一个查询语句里面，goods_code是取的s.goods_code,后面一个取的是t.goods_code.虽然值一样，但是前面一个联合查询却查询不出来，有点诡异。
解决方法：换成nvl2, 将上面代码里面的 nvl(t.goods_code,s.goods_code)换成nvl2(t.goods_code, t.goods_code, s.goods_code)上面存在的问题即可解决。
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原文地址：http://www.cnblogs.com/tarbitrary/p/4766641.html
