Mysql 对比查询比较

mysql--------
select a.dname,
max(if(b.mon='一月份',b.yj,0)) 一月份,
max(if(b.mon='二月份',b.yj,0)) 二月份,
max(if(b.mon='三月份',b.yj,0)) 三月份
from t2 a  left join t1 b on a.dep=b.dep
group by dname

mysql-------
select a.dname,
sum(case when b.mon='一月份' then b.yj else 0 end) 一月份,
sum(case when b.mon='二月份' then b.yj else 0 end) 二月份,
sum(case when b.mon='三月份' then b.yj else 0 end) 三月份
from t2 a left join t1 b on a.dep=b.dep
group by dname


oracle------注：decode的方法与mysql的不同
select a.dname,
max(decode(b.mon,'一月份',b.yj,0) 一月份，
max(decode(b.mon,'二月份',b.yj,0) 二月份，
max(decode(b.mon,'三月份',b.yj,0) 三月份)
from table2 a left join table1 b on a.dep=b.dep
group by dname