I have the following data frames: print(df_a) mukey DI PI 0 100000 35 14 1 1000005 44 14 2 1000006 44 14 3 1000007 43 13 4 1000008 43 13 print(df_b) mukey niccdcd 0 190236 4 1 190237 6 2 190238 7 3 190239 4 4 190240 7 When I try to join these data … Read more
This follows this prior question, which was answered. I actually discovered I could remove a join from that query, so now the working query is start_cards = DeckCard.find :all, :joins => [:card], :conditions => [“deck_cards.deck_id = ? and cards.start_card = ?”, @game.deck.id, true] This appears to work. However, when I try to move these DeckCards … Read more
Are JOIN queries faster than several queries? (You run your main query, and then you run many other SELECTs based on the results from your main query) I’m asking because JOINing them would complicate A LOT the design of my application If they are faster, can anyone approximate very roughly by how much? If it’s … Read more
What is the difference between a natural join and an inner join? 11 Answers 11
This question already has answers here: What is the difference between “INNER JOIN” and “OUTER JOIN”? (27 answers) Closed 1 year ago. I know about joins in SQL Server. For example. There are two tables Table1, Table2. Their table structures are the following. create table Table1 (id int, Name varchar (10)) create table Table2 (id … Read more
Is it possible to join the results of 2 sql SELECT statements in one statement? I have a database of tasks where each record is a separate task, with deadlines (and a PALT, which is just an INT of days from start to deadline. Age is also an INT number of days.) I want to … Read more
Disregarding performance, will I get the same result from query A and B below? How about C and D? — A select * from a left join b on <blahblah> left join c on <blahblan> — B select * from a left join c on <blahblah> left join b on <blahblan> — C select * … Read more
What is a SQL JOIN and what are different types? 6 Answers 6
Please help me understand where to use a regular JOIN and where a JOIN FETCH. For example, if we have these two queries FROM Employee emp JOIN emp.department dep and FROM Employee emp JOIN FETCH emp.department dep Is there any difference between them? If yes, which one to use when? 6 Answers 6
Suppose I have two DataFrames like so: left = pd.DataFrame({‘key1’: [‘foo’, ‘bar’], ‘lval’: [1, 2]}) right = pd.DataFrame({‘key2’: [‘foo’, ‘bar’], ‘rval’: [4, 5]}) I want to merge them, so I try something like this: pd.merge(left, right, left_on=’key1′, right_on=’key2′) And I’m happy key1 lval key2 rval 0 foo 1 foo 4 1 bar 2 bar 5 … Read more
