My question is the same as in the title: when we are joining two data frames why
FROM statement doesn’t need both data frames names?
SELECT c.*, f.name country_name FROM facts f
INNER JOIN cities c ON c.facts_id = f.id
from has just
facts instead of
Does it matter which one I choose (when I choose just one)?
The simple answer:
FROM doesn’t need two dataframes. Consider the simplest of queries:
This is a perfectly valid query and
FROM needs only one dataframe. It’s only when we want to
JOIN two dataframes that we actually need the name of another dataframe. Therefore we name the second dataframe only when we use a
JOIN statement and the name of the second dataframe is part of the
Yes, it will matter which one you choose if you’re only choosing one – you will need to choose the one that has the features you’re looking to query. ie the features you place in the
…so when I join two, it doesn’t matter which I choose in
FROM statement? Am I understand this particular case correctly?
The only time order doesn’t matter is when doing an inner join. For all other types of joins, it will matter which is in the
FROM statement and which one is in the
Check out this stackoverflow post for a more in depth explanation.