code:

a b    c
1 0.4  a
1 0.2  b
1 0.7  c
1 0.3  d
2 0.3  e
2 0.2  f
2 0.1  g
2 0.4  h
3 0.8  i
3 0.9  j
3 0.3  k
3 0.7  l
4 0.9  m
4 0.8  n
4 0.3  o
4 0.1  p

code:

a c
1 b
2 g
3 k
4 p

code:
SELECT a, c
  FROM (SELECT ROW_NUMBER () OVER (PARTITION BY a ORDER BY b) AS r, a, c
          FROM tabl) tt
 WHERE r = 1

code:
sqlite> select q.a, q.c from x q left join x w on (q.a = w.a and q.b > w.b) where w.a is null;
a c
1 b
2 g
3 k
4 p

code:

select a,  (select c from #Temp e where a = t.a and b = t.b)
from (
select c.a a, min(c.b) b
from #temp c
group by c.a) t

code:

select a,  (select c from #Temp e where a = t.a and b = t.b)
from (
select c.a a, max(c.b) b
from #temp c
group by c.a) t

code:

select a,  (select min(c) from #Temp e where a = t.a and b = t.b)
from (
select c.a a, min(c.b) b
from #temp c
group by c.a) t

code:

select t.a, p.c
from (
select c.a a, min(c.b) b
from #temp c
group by c.a) t join #temp p on t.a= p.a and t.b = p.b