Having子句

create table promotions
(
name varchar2(20),
promo_id number(6),
promo_name varchar2(30),
promo_subcategory varchar2(30),
promo_category varchar2(30),
promo_cost number(10,3),
promo_begin_date date,
promo_end_date date
);

此语句居然不会报错
select promo_category,  sum(promo_cost)
from promotions
group by promo_category
having min(promo_end_date-promo_begin_date) > 30;

可以理解为
select promo_category,  sum(promo_cost),min(promo_end_date-promo_begin_date)
from promotions
group by promo_category
having min(promo_end_date-promo_begin_date) > 30;


验证一下：
--第一组符合条件
insert into promotions(promo_category,promo_cost,promo_end_date,promo_begin_date) values('A',1, sysdate,sysdate-31);
insert into  promotions(promo_category,promo_cost,promo_end_date,promo_begin_date) values ('A',2, sysdate, sysdate -32 );

--第二组不符合条件
insert into promotions(promo_category,promo_cost,promo_end_date,promo_begin_date) values('B',5, sysdate, sysdate -29);
insert into promotions(promo_category,promo_cost,promo_end_date,promo_begin_date) values('B',4, sysdate, sysdate -32);

--第三组不符合条件
insert into promotions(promo_category,promo_cost,promo_end_date,promo_begin_date) values('C',5, sysdate, sysdate -29);
insert into promotions(promo_category,promo_cost,promo_end_date,promo_begin_date) values('C',6, sysdate, sysdate -28);

commit;

执行查询语句，只有第一组会被筛选出来

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转载于:http://blog.itpub.net/31142205/viewspace-2124030/