greatest-n-per-group

I have two SQLite tables like this: AuthorId | AuthorName ---------------------- 1 | Alice 2 | Bob 3 | Carol ... | .... BookId | AuthorId | Title ---------------------------------- 1 | 1 | aaa1 2 | 1 | aaa2 3 | 1 | aaa3 4 | 2 | ddd1 5 | 2 | ddd2 ... | ... | ... 19 | 3 | fff1 20 | 3 | fff2 21 | 3 | fff3 22 | 3 | fff4 I want to make a SELECT query that will return the first N (e.g. two) rows for each AuthorId, ordering by Title ("Select the first two books of each author"). Sample output: BookId | AuthorId | AuthorName | Title ------------------------------------------ 1 | 1 | Alice | aaa1 2 | 1

This question already has an answer here: SQL select only rows with max value on a column [duplicate] 27 answers Let's say I have a table called messages with the columns: id | from_id | to_id | subject | message | timestamp I want to get the latest message from each user only, like you would see in your FaceBook inbox before you drill down into the actual thread. This query seems to get me close to the result I need: SELECT * FROM messages GROUP BY from_id However the query is giving me the oldest message from each user and not the newest. I can't figure this one out. You should find out last

I want to get some column based on another column Example table: | BlilCode | BlilShortName | BatchWeigth | BillVersion | BlilMaxTime | +----------+---------------+-------------+-------------+-------------+ | 5502 | aaa | 1.00 | 1 | 360 | | 5502 | aaa | 2.00 | 2 | 240 | | 5510 | bbb | -32.94 | 2 | 360 | | 5510 | bbb | 1.00 | 1 | 360 | | 5510 | bbb | 36.37 | 3 | 3600 | but I want to get the rows where BillVersion is max for every BlilCode is max Expected result | BlilCode | BlilShortName | BatchWeigth | BillVersion | BlilMaxTime | +----------+---------------+-------------+-------------+--------

I'm trying to get the most recent record for a single customer on a table. Example: ID Customer City Amount 1 Cust001 City1 2 2 Cust001 City2 3 3 Cust001 City1 1 4 Cust001 City2 1 5 Cust001 City2 3 6 Cust001 City3 1 7 Cust001 City3 1 8 Cust002 City1 2 9 Cust002 City1 1 10 Cust002 City2 3 11 Cust002 City1 2 12 Cust002 City2 1 13 Cust002 City3 2 14 Cust002 City3 3 15 Cust003 City1 1 16 Cust003 City2 3 17 Cust003 City3 2 Please note that the table also has created_at and updated_at fields. I omitted those fields for simplicity. In the end I want my query to return for Cust001: ID Customer City

I have 3 queries: table: pageview SELECT event_id, count(*) AS pageviews FROM pageview GROUP BY event_id ORDER BY pageviews DESC, rand() LIMIT 1000 table: upvote SELECT event_id, count(*) AS upvotes FROM upvote GROUP BY event_id ORDER BY upvotes DESC, rand() LIMIT 1000 table: attending SELECT event_id, count(*) AS attendants FROM attending GROUP BY event_id ORDER BY attendants DESC, rand() LIMIT 1000 I'd like to combine the event_id s of all 3 queries ordered by amount and then choose the top 5. How do I do that? EDIT: HERE IS WHAT I DID TO MAKE IT HAPPEN: SELECT event_id, sum(amount) AS total

select * from records where id in ( select max(id) from records group by option_id ) This query works fine even on millions of rows. However as you can see from the result of explain statement: QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------- Nested Loop (cost=30218.84..31781.62 rows=620158 width=44) (actual time=1439.251..1443.458 rows=1057 loops=1) -> HashAggregate (cost=30218.41..30220.41 rows=200 width=4) (actual time=1439.203..1439.503 rows=1057 loops=1) -> HashAggregate (cost=30196.72.

I have this table : And I would like to make a request that would return for each deal_id the row with the highest timestamp , and the corresponding status_id . So for this example, I would have returned 2 rows : 1226, 3, 2009-08-18 12:10:25 1227, 2, 2009-08-17 14:31:25 I tried to do it with this query SELECT deal_id, status_id, max(timestamp) FROM deal_status GROUP BY deal_id but it would return the wrong status_id : 1226, 1, 2009-08-18 12:10:25 1227, 1, 2009-08-17 14:31:25 without a single primary key field, I think your best bet is: select * from deal_status inner join (select deal_id as

I have a table like this: Column | Type | Modifiers ---------+------+----------- country | text | food_id | int | eaten | date | And for each country, I want to get the food that is eaten most often. The best I can think of (I'm using postgres) is: CREATE TEMP TABLE counts AS SELECT country, food_id, count(*) as count FROM munch GROUP BY country, food_id; CREATE TEMP TABLE max_counts AS SELECT country, max(count) as max_count FROM counts GROUP BY country; SELECT country, max(food_id) FROM counts WHERE (country, count) IN (SELECT * from max_counts) GROUP BY country; In that last statement, the

I'm trying to get the ip, user, and most recent timestamp from a table which may contain both the current ip for a user and one or more prior ips. I'd like one row for each user containing the most recent ip and the associated timestamp. So if a table looks like this: username | ip | time_stamp --------------|----------|-------------- ted | 1.2.3.4 | 10 jerry | 5.6.6.7 | 12 ted | 8.8.8.8 | 30 I'd expect the output of the query to be: jerry | 5.6.6.7 | 12 ted | 8.8.8.8 | 30 Can I do this in a single sql query? In case it matters, the DBMS is Postgresql. Try this: Select u.[username] ,u.[ip] ,q.