greatest-n-per-group

This question already has an answer here: Fetch the row which has the Max value for a column 34 answers Oracle SQL query: Retrieve latest values per group based on time [duplicate] 2 answers Get top results for each group (in Oracle) 5 answers GROUP BY with MAX(DATE) [duplicate] 6 answers I am having a hard time doing this without searching the same table at least twice in order to grab the max row, and then grab the value for that row. The table in question is quite big so this is unacceptable. Here is what my table might look like: SCORES ID ROUND SCORE 1 1 3 1 2 6 1 3 2 2 1 10 2 2 12 3 1 6

I have the following data in my database: |NO | model | date | +---+-------+----------+ |1 | bee |2011-12-01| |2 | bee |2011-12-05| |3 | bee |2011-12-12| |4 | tar |2011-12-13| I want to get the latest date of each model group: | model | date | +-------+----------+ | bee |2011-12-12| | tar |2011-12-13| I tried: SELECT model, date FROM doc WHERE date ........????? //what is the next? GROUP BY model Are you looking for the max date for each model? SELECT model, max(date) FROM doc GROUP BY model If you're looking for all models matching the max date of the entire table... SELECT model, date FROM

My table looks like this (and I'm using MySQL): m_id | v_id | timestamp ------------------------ 6 | 1 | 1333635317 34 | 1 | 1333635323 34 | 1 | 1333635336 6 | 1 | 1333635343 6 | 1 | 1333635349 My target is to take each m_id one time, and order by the highest timestamp. The result should be: m_id | v_id | timestamp ------------------------ 6 | 1 | 1333635343 34 | 1 | 1333635336 And i wrote this query: SELECT * FROM table GROUP BY m_id ORDER BY timestamp DESC But, the results are: m_id | v_id | timestamp ------------------------ 34 | 1 | 1333635323 6 | 1 | 1333635317 I think it causes because

For an example, I would like to select id with max date group by category, the result is: 7, 2, 6 id category date 1 a 2013-01-01 2 b 2013-01-03 3 c 2013-01-02 4 a 2013-01-02 5 b 2013-01-02 6 c 2013-01-03 7 a 2013-01-03 8 b 2013-01-01 9 c 2013-01-01 May I know how to do this in PostgreSQL? This is a perfect use-case for DISTINCT ON (Postgres specific extension of standard DISTINCT ): SELECT DISTINCT ON (category) id -- , category, date -- add any other column (expression) from the same row FROM tbl ORDER BY category, "date" DESC; Careful with descending sort order. If the column can be NULL,

This is a product table and have few million of records. I want to list record as below: Normally I use: SELECT id, product_name, store_id FROM product GROUP BY store_id ORDER BY id. Currently having SQL performance issue. I need SQL query to output result like this. John Woo There are many alternatives to solves this, one which I recommend is to have joined a subquery which separately gets the latest ID ( assuming that the column is AUTO_INCREMENT ed ) for each store_ID . SELECT a.* FROM tableName a INNER JOIN ( SELECT store_ID, MAX(ID) max_ID FROM tableName GROUP BY store_ID ) b ON a.store