Pulling max values grouped by a variable with other columns in SQL - sql

Question

Say I have three columns in a very large table: a timestamp variable (last_time_started), a player name (Michael Jordan), and the team he was on the last time he started (Washington Wizards, Chicago Bulls), how do I pull the last time a player started, grouped by player, showing the team? For example:
if I did
select max(last_time_started), player, team
from table
group by 2
I would not know which team the player was on when he played his last game, which is important to me.

Answer 1

In Postgres the most efficient way is to use distinct on():
SELECT DISTINCT ON (player)
last_time_started,
player,
team,
FROM the_table
ORDER BY player, last_time_started DESC;
Using a window function is usually the second fastest solution, using a join with a derived table is usually the slowest alternative.

Answer 2

Here's a couple of ways to do this in Postgres:
With windowing functions:
SELECT last_time_started, player, team
FROM
(
SELECT
last_time_started,
player,
team,
CASE WHEN max(last_time_started) OVER (PARTITION BY PLAYER) = last_time_started then 'X' END as max_last_time_started
FROM table
)
WHERE max_last_time_started = 'x';
Or with a correlated subquery:
SELECT last_time_started, player, team
FROM table t1
WHERE last_time_started = (SELECT max(last_time_started) FROM table WHERE table.player = t1.player);

Answer 3

Try this solution
select s.*
from table s
inner join (
select max(t.last_time_started) as last_time_started, t.player
from table t
group by t.player) v on s.player = t.player and s.last_time_started = t.last_time_started
Also this approach should be faster, because it does not contain join
select v.last_time_started,
v.player,
v.team
from (
select t.last_time_started,
t.player,
t.team,
row_number() over (partition by t.player order by last_time_started desc) as n
from table t
) v
where v.n = 1