WITH语句

池塘边上有牛和鹅若干，小华总共看到15个头42条腿，请问牛和鹅各有多少？
• 分析：若全是鹅，则腿总共30只，显然不够，若全是牛，则腿总共60只，显然多了
with a as (select 1 from dual union all select 1 from dual),b as (select rownum n from a, a, a, a)
 --构造出16条记录，代表1到16
select x.n num_of_bull, y.n num_of_goose from b x, b y where x.n*4+y.n*2=42 and x.n+y.n=15;