select count(*) from db1 where grade = 0;
select count(*) from db1 where grade = 1;
select count(*) from db1 where grade = 2;
select count(*) from db1 where grade = 3;
以上4条sql，合成一条可以实现吗？
为什么在mysql中可以这样实现：
SELECT (SELECT COUNT(*) FROM db1 WHERE gread = 1) AS g1,(SELECT COUNT(*) FROM db1WHERE gread = 2) AS g2;
而DB2中不可以。。。
select grade,count(*) from db1 where grade = 0 or grade = 1 or grade = 2 or grade = 3 group by grade;
这样写貌似好一点..mysql,db2,oracle等都通用..
[code="sql"]
select
count(case when grade = 1 then 1 else null end) as g1,
count(case when grade = 2 then 1 else null end) as g2,
count(case when grade = 3 then 1 else null end) as g3,
count(case when grade = 4 then 1 else null end) as g4
from db1;
[/code]