Assuming relatively few rows in options for many rows in records. Typically, you would have a look-up table options that is referenced from records.option_id, ideally with a foreign key constraint. If you don’t, I suggest to create one to enforce referential integrity: CREATE TABLE options ( option_id int PRIMARY KEY , option text UNIQUE NOT … Read more
If you can assume that artist IDs increment over time, then the MIN(artist_id) will be the earliest. So try something like this (untested…) SELECT * FROM feeds f LEFT JOIN artists a ON a.artist_id = ( SELECT MIN(fa.artist_id) a_id FROM feeds_artists fa WHERE fa.feed_id = f.feed_id ) a
We can try data.table. Convert the ‘data.frame’ to ‘data.table’ (setDT(df1)), grouped by ‘group’ , we get the cummax of ‘var’ and assign (:=) it to a new variable (‘curMax’) library(data.table) setDT(df1)[, curMax := cummax(var), by = group] As commented by @Michael Chirico, if the data is not ordered by ‘time’, we can do that in … Read more
I see many people use subqueries or else window functions to do this, but I often do this kind of query without subqueries in the following way. It uses plain, standard SQL so it should work in any brand of RDBMS. SELECT t1.* FROM mytable t1 LEFT OUTER JOIN mytable t2 ON (t1.UserId = t2.UserId … Read more
MySQL 8.0 now supports windowing functions, like almost all popular SQL implementations. With this standard syntax, we can write greatest-n-per-group queries: WITH ranked_messages AS ( SELECT m.*, ROW_NUMBER() OVER (PARTITION BY name ORDER BY id DESC) AS rn FROM messages AS m ) SELECT * FROM ranked_messages WHERE rn = 1; This and other approaches … Read more
At first glance… All you need is a GROUP BY clause with the MAX aggregate function: SELECT id, MAX(rev) FROM YourTable GROUP BY id It’s never that simple, is it? I just noticed you need the content column as well. This is a very common question in SQL: find the whole data for the row … Read more