SQL 不使用 ALIAS 列進行計算

Question

問題陳述 - 從出租車服務的給定行程和用戶表中，編寫查詢以返回 10 月份前兩天的取消率，四舍五入到小數點后兩位，對於不涉及被禁止的乘客或司機的行程。

Oracle SQL 上的問題代碼。

create table trips (trip_id int, rider_id int, driver_id int, status varchar2(200), request_date date);
insert into trips values (1, 1, 10, 'completed', to_date ('2020-10-01', 'YYYY/MM/DD'));
insert into trips values (2, 2, 11, 'cancelled_by_driver', to_date ('2020-10-01', 'YYYY/MM/DD'));
insert into trips values (3, 3, 12, 'completed', to_date ('2020-10-01', 'YYYY/MM/DD'));
insert into trips values (4, 4, 10, 'cancelled_by_driver', to_date ('2020-10-02', 'YYYY/MM/DD'));
insert into trips values (5, 1, 11, 'completed', to_date ('2020-10-02', 'YYYY/MM/DD'));
insert into trips values (6, 2, 12, 'completed', to_date ('2020-10-02', 'YYYY/MM/DD'));
insert into trips values (7, 3, 11, 'completed', to_date ('2020-10-03', 'YYYY/MM/DD'));

create table users (user_id int, banned varchar2(200), type varchar2(200));
insert into users values (1, 'no', 'rider');
insert into users values (2, 'yes', 'rider');
insert into users values (3, 'no', 'rider');
insert into users values (4, 'no', 'rider');
insert into users values (10, 'no', 'driver');
insert into users values (11, 'no', 'driver');
insert into users values (12, 'no', 'driver');

我的解決方案代碼如下。 但是，我收到以下錯誤。 有人可以幫忙嗎？

ORA-00904: "TOTAL_TRIPS": invalid identifier

解決方案代碼：

select request_date, (1-(trips_completed/total_trips)) as "cancel_rate"
from
((
select request_date,
sum(case when status = 'completed' then 1 else 0 end) as "trips_completed",
sum(case when status = 'cancelled_by_driver' then 1 else 0 end) as "trips_cancelled",
sum(case when status = 'cancelled_by_driver' then 1 when status= 'completed' then 1 else 0 end) as "total_trips"
from 
(
select t.rider_id, t.driver_id, t.status, t.request_date, u.banned as "not_banned_rider", u.banned as "not_banned_driver"
from trips t
join users u
on t.rider_id=u.user_id
where u.banned='no'
)
group by request_date
having request_date <> to_date ('2020-10-03', 'YYYY/MM/DD')
));

Answer 1

首先，不要將標識符放在雙引號中。 他們只是把查詢弄得亂七八糟。

其他一些需要解決的問題：

• 不需要兩個級別的子查詢。
• 學習使用正確的date文字語法。
• 我想你想要<而不是<> 。

所以這表明：

select request_date, (1-(trips_completed/total_trips)) as cancel_rate
from (select request_date,
             sum(case when status = 'completed' then 1 else 0 end) as trips_completed,
             sum(case when status = 'cancelled_by_driver' then 1 else 0 end) as trips_cancelled,
             sum(case when status = 'cancelled_by_driver' then 1 when status = 'completed' then 1 else 0 end) as total_trips
      from trips t join
           users u
           on t.rider_id = u.user_id
      where u.banned = 'no' and
            t.request_date < date '2020-10-03'
      group by request_date 
     ) rd;

這可以使用avg()進一步簡化：

select request_date,
       avg(case when status = 'completed' then 1 else 0 end) as cancel_rate
from trips t join
     users u
     on t.rider_id = u.user_id
where u.banned = 'no' and
      request_date < date '2020-10-03'
group by request_date ;

注意：這解決了修復問題中的查詢。 它實際上並沒有正確回答這個問題，原因如下：

• 我很確定這個問題需要一個取消率，而不是兩個日期一個。
• 它沒有考慮被禁止的司機。
• 我不確定如何處理“用戶取消”。

Answer 2

ORA-00904: "TOTAL_TRIPS": 無效標識符

只是意味着寫的“total_trips”是無效的

只需使用 total_trips （不帶引號）