Question

Working on postgres SQL.

I have a table with a column that contains values of the following format:

Set1/Set2/Set3/…

Seti can be a set of values for each i. They are delimited by ‘/’.

I would like to show distinct entries of the form set1/set2 and that is – I would like to trim or truncate the rest of the string in those entries.
That is, I want all distinct options for:

Set1/Set2

A regular expression would work great: I want a substring of the pattern: .*/.*/

to be displayed without the rest of it.

I got as far as:

select distinct column_name from table_name

but I have no idea how to make the trimming itself.

Tried looking in w3schools and other sites as well as searching SQL trim / SQL truncate in google but didn’t find what I’m looking for.

Thanks in advance.

Answer 1

If they really are that regular you could use substring; for example:

=> select substring('Set1/Set2/Set3/' from 1 for 9);
 substring 
-----------
 Set1/Set2
(1 row)

There is also a version of substring that understands POSIX regular expressions if you need a little more flexibility.

The PostgreSQL online documentation is quite good BTW:

http://www.postgresql.org/docs/current/static/index.html

and it even has a usable index and sensible navigation.

---

If you want to use .*/.* then you’d want something like substring(s from '[^/]+/[^/]+'), for example:

=> select substring('where/is/pancakes/house?' from '[^/]+/[^/]+');
 substring 
-----------
 where/is
(1 row)