从SQL查询中删除重复项以进行保留选择

Question

I have the following tables:

• rtable
• reservation

Now rtable has the following columns:

• id int primary key
• seats int
• position varchar(10)

And reservation has the following columns:

• reservation_id int primary key
• table_id int foreign key(references rtable.id)
• reservation_date date
• start_hour

Now I want to perform the following query: use restaurant;

select id,position,seats from rtable,reservation 
            where (seats >= 6 and position = 'Indoors') 
            and (not exists(select * from reservation where table_id = id) or(
            (exists(select 1 from reservation where table_id = id) and
                (reservation_date != '2017-05-23' or reservation.start_hour != 16))))

However this query returns duplicates for rtable.id. Is there any way to remove these duplicates

Here is an example output:

Answer 1

If you are using foreign key then why you are not using joins. And why you are checking so much condition, please check this:

    SELECT rt.id, rt.position, rt.seats FROM rtable rt LEFT JOIN reservation res
    ON rt.id = res.table_id AND rt.seats >=6 AND rt.position = 'Indoors' AND
    (res.reservation_date != '2017-05-23' AND res.start_hour != 16)

Tell me if this solved your issue or give me dataset and condition, I will help you out.

Answer 2

Try this:

select distinct id,position,seats from rtable,reservation 
            where (seats >= 6 and position = 'Indoors') 
            and (not exists(select * from reservation where table_id = id) or(
            (exists(select 1 from reservation where table_id = id) and
                (reservation_date != '2017-05-23' or reservation.start_hour != 16))))