I want to use PostgreSQL’s functionality in order to obtain the row that has the longest path in either ind or tar column, for the same id, ind_id and tar_id.

For example:

At the table below, since rows 1, 2, 3 have the same id=1, ind_id=2 and tar_id=3, I want to only take the 3rd row because the array tar={7,8,9}, is longer than {7,8} (2nd row) and {7} (1st row).

Similarly, rows #4 and #5, have the same values for id, ind_id and tar_id, and since the length of the array in column ind is longer in row #5, I want to keep this row only, and drop row #4.

Since I am a newbie in the world of PostgreSQL, can someone give me a hint how to do that?

      text        id       ind_id       tar_id       ind       tar

1     bla bla      1        2             3          {4}       {7}
2     bla bla      1        2             3          {4}       {7,8}
3     bla bla      1        2             3          {4}       {7,8,9}      
4     bla bla      1        2            33          {5}       {10}    
5     bla bla      1        2            33          {5,6,7}   {10}  

>Solution :

Use distinct on and order by id, ind_id, tar_id and the greatest array length of ind and tar.

select distinct on (id, ind_id, tar_id) *
from the_table
order by id, ind_id, tar_id, 
 greatest(array_length(ind::integer[], 1), array_length(tar::integer[], 1)) desc;