SQL - Selecting rows with a column value greater than the rows before it

Question

I'm curious on the best way to write a query.

I have a table of ids and values. I would like to exclude rows where val is less than val in all of the rows with a lower ID.

I was playing with joining this table to itself on id-1 but that didn't work all of the time.

Some sample data

CREATE TEMP TABLE new_temp_table (
    id integer, 
    val integer
);

INSERT INTO new_temp_table (id, val)
VALUES (0, 300),
       (1, 150),
       (2, 100), 
       (3, 200),
       (4, 320),
       (5, 120),
       (6, 220),
       (7, 340);

I want the following output.

--- id --- val 
--- 0  --- 300
--- 4  --- 320
--- 7  --- 340 

Any help/direction would be appreciated.

Answer 1

With NOT EXISTS:

select t.* from new_temp_table t
where not exists (
  select 1 from new_temp_table
  where id < t.id and val > t.val
)  

See the demo .
Results:

| id  | val |
| --- | --- |
| 0   | 300 |
| 4   | 320 |
| 7   | 340 |

Answer 2

From what you describe, you can use window functions to calculate the max on all the preceding rows and then filter based on that:

select id, val
from (select ntt.*, max(val) over (order by id rows between unbounded preceding and 1 preceding) as preceding_max
      from new_temp_table ntt
     ) t
where preceding_max is null or val > preceding_max;

Here is a db<>fiddle.

Note: It is tempting to write this logic without the window specification as:

select id, val
from (select ntt.*, max(val) over (order by id) as preceding_max
      from new_temp_table ntt
     ) t
where preceding_max is null or val >= preceding_max;

However, this will return rows where the max equals an earlier maximum.

Answer 3

I would do:

select
  id, val, max_prev_val
from (
  select
    id,
    val,
    max(val) over(order by id rows between unbounded preceding and 1 preceding) 
      as max_prev_val
  from new_temp_table
) x
where val >= max_prev_val or max_prev_val is null  

Result:

id           val          max_prev_val  
----------------------------------------
0            300          <null>        
4            320          300           
7            340          320