So I passed this lesson but am not understanding this. How does the flight table know which airport the flight is leaving from? Shouldn’t there be a primary and foreign key to join the two tables together?
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what was the FULL code you used…
In the these exercises we are using SQLite
You could also read the meaning in an Oracle-SQL environment
sql non correlated query site:oracle.com
Please re-read the question I’m asking. The problem is not with my code. My code is correct and I passed the lesson. The problem is my understanding of the lesson.
I am confused as to how the flight table knows which airport the flight is leaving from? Shouldn’t there be a primary and foreign key to join the two tables together?
The link to the exercise is in the original post.
As we are using SQLite we could analyze the used Database
+++ show all table defintions
select * from sqlite_master;
If you use the Query
WHERE origin in (
WHERE elevation > 2000);
the Database-engine will create a list of airport code’s
( each Airport has its own unique code )
WHERE elevation > 2000
In the flights table they use these unique-airport-code’s
in the columns
And this case we use
WHERE origin in (created list of airport codes)
And if we read through the definitions
Correlated subquery is an inner query referenced by main query (outer query) such that inner query considered as being excuted repeatedly.
non-correlated subquery is a sub query that is an independent of the outer query and it can executed on it’s own without relying on main outer query.
plain subquery is not dependent on the outer query
we can conclude we are using a non-correlated query
Thanks for the explanation
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