Write element's ancestry to Postgres table from adjacency list

Question

I want to write a 1 to n-hierarchy that\'s stored as an adjacency list to a table that lists each of an element\'s ancestors. I\'m using a Postgres database (Postgres 10, but th

Answer 1

if the position of the object is not changed in time (i.e. if it was put from the beginning on level 6 it will stay on that level forever) you can introduce some sane id with 7 numbers, showing 7 levels, separated by lets say semicolon(:):

'1:1:1:1:1:1:1'

and then introduce some functional indexes, like:

CREATE INDEX level1_idx ON main_table USING (regexp_split_to_array(id, '\\:')[1])
CREATE INDEX level2_idx ON main_table USING (regexp_split_to_array(id, '\\:')[2])
CREATE INDEX level3_idx ON main_table USING (regexp_split_to_array(id, '\\:')[3])

then you can alaways make an efficient query:

SELECT id, regexp_split_to_array(id, '\\:')[1] as level1, regexp_split_to_array(id, '\\:')[2] as level2, ...
ORDER BY level1, level2, level3 ...