oracle 多列求和

第一种：

select sum(decode(count1,null,0,count1) +decode(count2,null,0,count2)
+decode(count3,null,0,count3)) a from test_table

第二种：

select sum (case when count1 is not null then count1 when 
count2 is not null then count2 when count3 is not null 
then count3 else '0' end ) a from test_table