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Databases SQL Basics Finding the Data You Want Filtering by Dates

Luis Manuel Lopez Hidalgo
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Luis Manuel Lopez Hidalgo
Full Stack JavaScript Techdegree Student 23,195 Points
Posted by Luis Manuel Lopez Hidalgo
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Luis Manuel Lopez Hidalgo
Full Stack JavaScript Techdegree Student 23,195 Points

Not a question but a comment. I think in the last part of the video what we want is the patron_id and not the id.

I think we need the patron_id because they are the people we are looking to send an email.

1 Answer

Jason Anello
Jason Anello
Courses Plus Student 94,610 Points

Hi Luis,

I think these are the 2 queries you're referring to:

SELECT * FROM loans WHERE return_by > "2015-12-18";

SELECT first_name, email FROM patrons WHERE id = 1 OR id = 3;

It's correct to use id in the second query because Andrew is querying the patrons table which doesn't have a patron_id column but it does have an id column used as the primary key.

The loans table does have a patron_id column. This is used as a foreign key on the patrons table. It creates a relationship between the 2 tables. The patron_id column in the loans table corresponds to the id column in the patrons table.

With the 1st query Andrew looked at the patron_id column from the loans table to discover that patrons 1 and 3 haven't returned their books yet. Andrew then searches for those id's in the patrons table (using the id column) to get their contact information.