sql优化：查询时加判断

Question

1.数据表的结构：
订单ID：orderid,
用户ID：memberid,
下单日期：order_date

2.需求：需要查询出2017-04月下单的记录（orderid,memberid），如果当前记录的用户有在4月份之前下过单，第三列是否订购过：是，4月份之前没有下过单的，第三列是否订购过：否，

3.已经写好的sql:

SELECT orderid,memberid, '是' AS '是否订购过' FROM ordersum WHERE order_date >= '2017-04-01' AND order_date < '2017-05-01' AND memberid IN (SELECT memberid FROM ordersum WHERE order_date < '2017-04-01')
UNION
SELECT orderid,memberid, '否' AS '是否订购过' FROM ordersum WHERE order_date >= '2017-04-01' AND order_date < '2017-05-01' AND memberid  NOT IN (SELECT memberid FROM ordersum WHERE order_date < '2017-04-01')
ORDER BY orderid

可以实现该需求，只是感觉还有优化的空间，请大家帮忙看看，谢谢！

Answer 1

mysql 的 if 了解下。

Answer 2

select orderid, memberid, bool_judge from (select orderid, memberid, case when order_date <= '2017-04-01' then '是' else '否' end as bool_judge) as test where order_date >= '' and order_date <= ''