假设我在 MYSQL 中有以下表
Sailors (sid,sname,rating,age) where sid-> Sailor's id,
Reserves (sid,bid,day) where bid-> boat's id
<小时/>
我的查询是:-
Find names of the sailors who have sailed two different boats on the same day ?
首先,我尝试连接两个保留表副本并添加一个条件,即出价必须不同。
SELECT * FROM reserves R1,reserves R2 WHERE R1.day = R2.day AND R1.bid <> R2.bid;
我得到这样的输出:-
现在,查询需要水手的姓名
,因此我必须将水 watch 与结果表连接起来。
现在,我如何应用连接(条件是什么)操作来获得所需的结果?
最佳答案
drop table if exists sailors;
drop table if exists reserves;
create table sailors(sid int, sname varchar(3));
create table reserves(bid int,sid int, dt date);
insert into sailors values
(1,'abc'),(2,'def'),(3,'ghi');
insert into reserves values
(100,1,'2017-01-01'),(200,1,'2017-01-01'),
(100,1,'2017-01-02'),(100,1,'2017-01-02'),
(100,2,'2017-01-01'),(100,2,'2017-01-01'),(300,2,'2017-01-01'),
(100,2,'2017-01-03'),(200,2,'2017-01-04')
;
select s.sid,t.sname,s.dt
,group_concat(s.bid order by s.bid) boats
from
(
select r.sid,r.dt,r.bid,
if(concat(r.sid,r.dt,r.bid) <> @p, @rn:=1,@rn:=@rn+1) rn,
@p:=concat(r.sid,r.dt,r.bid) p
from (select @rn:=0,@p:='') rn,reserves r
order by r.sid,r.dt,r.bid
) s
join sailors t on t.sid = s.sid
where s.rn = 1
group by s.sid,s.dt
having instr(boats,',') > 0
+------+-------+------------+---------+
| sid | sname | dt | boats |
+------+-------+------------+---------+
| 1 | abc | 2017-01-01 | 100,200 |
| 2 | def | 2017-01-01 | 100,300 |
+------+-------+------------+---------+
2 rows in set (0.00 sec)
关于mysql - 如何在 MYSQL 中连接具有相同实例的相同表?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/43179623/