从多个表中获取新的数据表，然后对新数据表的字段进行计算求值。

select (Number01.N1/Number02.N2)  --get tow table_fields
from

(select count(A.field01)as N1 
from Table01 A,
Table02 B	
where A.field01=B.field02) Number01,  --like new Table

(select count(B.field02) as N2
from Table02 B) Number02   --like new Table

SQL中从不同表中链接数据计算