How to get count of two columns of a table based on PK of another table?
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I have two tables defined as:
CREATE TABLE airports ( code char(3) not null primary key, name varchar(100) not null, city varchar(50) not null, state varchar(5), country char(2) not null references fcountries(code) )
CREATE TABLE flights ( departure char(3) not null references airports(code), -- airport code arrival char(3) not null references airports(code), -- airport code dep_time time not null, airline char(2) not null references airlines(code) )
I need to get the number of flights departing from and arriving at an airport using postgres. So, I wrote
select code, count(departure) from airports join flights on flights.departure = airports.code group by code;
and for departure similarily,
select code, count(arrival) as Arrival from airports join flights on flights.arrival = airports.code group by code;
But I need to combine these two and get the arrival-departure count in the same result. I am not sure how to do it? I wrote this query
select code, count(departure), x.arrival from ( select count(arrival) as arrival from airports join flights on flights.arrival = airports.code group by code ) x, airports join flights on airports.code = flights.departure group by code, x.arrival order by code;
But the result is not correct as 'code' is repeated in this result. I am pretty new to sql and not sure how to write this.
I think alias t2 cannot be used like that after join that's why you are getting the error. Try this:
select t1.code, t1.count_departure, t2.count_arrival
select code, count(departure) count_departure
from airports join flights on flights.departure = airports.code
group by code
select code, count(arrival) as count_arrival
from airports join flights on flights.arrival = airports.code
group by code
) t2 on t1.code = t2.code;
SQL count column from another table, I have two tables in a database. The first select p.name, (select count(*) from relationships r where r.following = p.id) followers, (select count(*) from After the JOIN , any column with no NULL values will return the same result. We can try using two separate subqueries to find the two following counts: I have two tables in an SQL Server database, one with two columns and one with four: tbl_email_list. email_list_id int (PK) email_list_name varchar; tbl_email-details. email_uniq_id int (PK) email_list_id int (FK) email_address varchar; blacklist bit; I want to retrieve data in one query which should return. All the email lists from tbl_email_list;
The simplest method is a lateral join and
select v.code, count(*) as total, sum(is_departure) as num_departures, sum(is_arrival) as num_arrivals from flights cross join lateral (values (departure, 1, 0), (arrival, 0, 1) ) as v(code, is_departure, is_rrival) on f.departure = a.code group by v.code;
Note that the
airports is unnecessary, unless you actually want to bring in more information that you haven't mentioned in the question.
SQL join two tables related by a single column primary key or , To get 'item_name' and 'item_unit' from 'foods' table and 'company_name' and ' company_city' form 'company' table after a joining with� to a certain class, and the table has a PK based on two columns: (CLASS_ID, ITEM_CODE). Then I want to update rows with the same ITEM_CODE from one class, with rows of a matching ITEM_CODE, but from a different class, so the statement looks like this: update (select from items c1 inner join items c2 on c1.item_code=c2.item_code
You could use the two query as subquery and join
select t1.code, t1.count_departure, t2.count_arrival from ( select code, count(departure) count_departure from airports join flights on flights.departure = airports.code group by code ) t1 inner join ( select code, count(arrival) as count_arrival from airports join flights on flights.arrival = airports.code roup by code ) t2 on t1.code = t2.code ;
SQL Inner Join to Two or More Tables, Use it to combine columns from two or more tables via a join condition. you need to join the primary key of one table to the foreign key of another. All the examples for this lesson are based on Microsoft SQL Server Get started using these free tools with my Guide Getting Started Using SQL HAVING COUNT(PT. Suppose, we have two tables: t1 and t2. The following steps compare two tables and identify the unmatched records: First, use the UNION statement to combine rows in both tables; include only the columns that need to compare. The returned result set is used for the comparison.
A quite simple method is just to use a correlated COUNT subquery in the SELECT clause:
select a.code, (select count(*) from flights f where f.departure = a.code) as departures, (select count(*) from flights f where f.arrival = a.code) as arrivals from airports a;
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- update your question add that the related tables schema a proper data sample and the expected result
- and decide about the DBMS please.
- typo i guess.
group by codeinstead of
roup by code
- that I changed still the error is there.
- this gives error "syntax error near select" that is select after t2(select code....) I don't know why?
- answer updated .. wrong position fo rtable alias name