SQL select with case when and join table

Question

我在 sql (postgresql) 中有 2 个表

tbl1：

dates	roomid	stok
2021-03-15	A01	3
2021-03-16	A01	3
2021-03-17	A01	3

tbl2：

bookingcode	startdate	enddate	roomid
B001	2021-03-15	2021-03-17	A01

我的语法是这样的

select dates, tbl1.roomid,
case
    when dates between startdate and enddate - integer '1' then stok -1
else stok
end stok
from tbl1
join tbl2
on tbl1.roomid = tbl2.roomid  order by dates asc

当预订数量为一个(tbl2)时，它匹配这样的结果。结果是正确的

dates	roomid	stok
2021-03-15	A01	2
2021-03-16	A01	2
2021-03-17	A01	3

但是当booking是2的时候，是这样的(tbl2)

bookingcode	startdate	enddate	roomid
B001	2021-03-15	2021-03-17	A01
B002	2021-03-15	2021-03-17	A01

结果是这样的，结果不合适

dates	roomid	stok
2021-03-15	A01	2
2021-03-15	A01	2
2021-03-16	A01	2
2021-03-16	A01	2
2021-03-17	A01	3
2021-03-17	A01	3

预订2时我想要的结果是这样的

dates	roomid	stok
2021-03-15	A01	1
2021-03-16	A01	1
2021-03-17	A01	3

谁能提出解决方案？

Answer 1

如果你需要更新数据库就这样做

UPDATE tbl1 SET stok = stok - (SELECT COUNT(*) FROM tbl2 WHERE tbl1.roomid = tbl2.roomid AND tbl1.dates >= tbl2.startdate AND tbl1.dates < tbl2.enddate);

不然

SELECT dates, roomid, stok - (SELECT COUNT(*) FROM tbl2 WHERE tbl1.roomid = tbl2.roomid AND tbl1.dates >= tbl2.startdate AND tbl1.dates < tbl2.enddate) FROM tbl1;