I have the following 3 tables: airport area booking And I have this query Running the query I get the error: I don’t understand what the problem is. I added an SQL Fiddle to play with: http://sqlfiddle.com/#!17/8a09f/1 Answer A subquery in the SELECT list is only allowed to return a single value. Not mu…
Tag: correlated-subquery
How to use the results of one query in the next query?
I have read answers here but I am still not quite sure how I would do this regarding two columns of a table and more than one result per query. So, the first query would look like this in my Node app: …
A question about a correlated subquery in SQL and AVG function
We need to query the DB for students whose points are greater than the average for the uni they go to. Now, in the handbook, it is used with GROUP BY clause, but I fail to understand why one is needed here at all if the universities are already grouped in the inner query’s WHERE condition. Could you som…
SQL ZOO List each continent and the name of the country that comes first alphabetically
Im confused why it could not be Can anyone please explain to me why it has to be x.continent=y.continent and not x.name=y.name ? Table Answer when you use x.name=y.name you are comparing country name from x with the country name from y if both instances have the same country name. That basically would just re…
Storing ‘Rank’ for Contests in Postgres
I’m trying to determine if there a “low cost” optimization for the following query. We’ve implemented a system whereby ‘tickets’ earn ‘points’ and thus can be ranked. In order to support analytical type of queries, we store the rank of every ticket (tickets can …
Get count of foreign key from multiple tables
I have 3 tables, with Table B & C referencing Table A via Foreign Key. I want to write a query in PostgreSQL to get all ids from A and also their total occurrences from B & C. Output desired (just the id from A & total count in B & C) : SQL so far SQL Fiddle : The
How do I use a subquery to show a column that has never been assigned to a different table?
I’m trying to Write a SELECT statement that returns the category_name column from the Categories table and returns one row for each category that has never been assigned to a product in the Products table. there are four categories in the categories table and only three have been used in the products ta…