Databases
StackOverflow2013
Postsdbo
POSQL - min() gets the lowest value, max() the highest, what if I want the 2nd (or 5th or nth) lowest value?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POSQL - min() gets the lowest value, max() the highest, what if I want the 2nd (or 5th or nth) lowest value?
    primarykey
    data
    text
    <p>The problem I'm trying to solve is that I have a table like this:</p> <p>a and b refer to point on a different table. distance is the distance between the points.</p> <pre><code>| id | a_id | b_id | distance | delete | | 1 | 1 | 1 | 1 | 0 | | 2 | 1 | 2 | 0.2345 | 0 | | 3 | 1 | 3 | 100 | 0 | | 4 | 2 | 1 | 1343.2 | 0 | | 5 | 2 | 2 | 0.45 | 0 | | 6 | 2 | 3 | 110 | 0 | .... </code></pre> <p>The important column I'm looking is a_id. If I wanted to keep the closet b for each a, I could do something like this:</p> <pre><code>update mytable set delete = 1 from (select a_id, min(distance) as dist from table group by a_id) as x where a_gid = a_gid and distance &gt; dist; delete from mytable where delete = 1; </code></pre> <p>Which would give me a result table like this:</p> <pre><code>| id | a_id | b_id | distance | delete | | 1 | 1 | 1 | 1 | 0 | | 5 | 2 | 2 | 0.45 | 0 | .... </code></pre> <p>i.e. I need one row for each value of a_id, and that row should have the lowest value of distance for each a_id.</p> <p>However I want to keep the 10 closest points for each a_gid. I could do this with a plpgsql function but I'm curious if there is a more SQL-y way.</p> <p>min() and max() return the smallest and largest, if there was an aggregate function like nth(), which'd return the nth largest/smallest value then I could do this in similar manner to the above.</p> <p>I'm using PostgeSQL.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USRory
    1. USRory
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POSQL - min() gets the lowest value, max() the highest, what if I want the 2nd (or 5th or nth) lowest value?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POSQL - min() gets the lowest value, max() the highest, what if I want the 2nd (or 5th or nth) lowest value?
      1. USJonathan
      1. VTFavorite
    3. VO
      singulars
      1. POSQL - min() gets the lowest value, max() the highest, what if I want the 2nd (or 5th or nth) lowest value?
      1. This table or related slice is empty.
      1. VTUpMod
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload