Join the query madness!
Of course, SQL does not stop with the the three keywords SELECT
, FROM
and WHERE
. Another very often used keyword is JOIN
, and more specifically INNER JOIN
. Take this call for example:
SELECT name, post
FROM users INNER JOIN tweats on users.id = user_id
WHERE date > "2015-09-19"
Here, the users
table is joined with the tweats
table. This is possible because the id
column in the users
table corresponds to the user_id
column in the tweats
table. Also notice how name
, from the users
table, and post
and date
, from the tweats
table, can be referenced to without problems.
Can you predict the outcome of the following query?
SELECT post, message
FROM tweats INNER JOIN comments on tweats.id = tweat_id
WHERE tweat_id = 77
A connection to the tweater
database is already available as con
; feel free to experiment!
This exercise is part of the course
Intermediate Importing Data in R
Hands-on interactive exercise
Turn theory into action with one of our interactive exercises
