Thread

1. BUG #17407: trim trims more than expected

   PG Bug reporting form <noreply@postgresql.org> — 2022-02-16T10:13:19Z

   The following bug has been logged on the website:
   
   Bug reference:      17407
   Logged by:          trim combined with substring from pattern for gives inconsistent output
   Email address:      unmesh.joshi126@gmail.com
   PostgreSQL version: 12.4
   Operating system:   Linux 5.15.4-051504-generic
   Description:        
   
   Expected output
   
   demo=# select trim ('nextval(''' from
   substring('nextval(''database_table_id_seq''::regclass)' from
   '%#"%_id_seq#"%' for '#' ));
            btrim         
   -----------------------
    database_table_id_seq
   (1 row)
   
   
   Unexpected output
   
   demo=# select trim ('nextval(''' from
   substring('nextval(''auth_table_id_seq''::regclass)' from '%#"%_id_seq#"%'
   for '#' ));
         btrim       
   ------------------
    uth_table_id_seq
   (1 row)
   
   

2. Re:BUG #17407: trim trims more than expected

   Sergei Kornilov <sk@zsrv.org> — 2022-02-16T11:03:41Z

   Hello
   But why don't you expect such a result?
   
   The letter a was definitely mentioned in the list of characters to trim.
   
   select trim('nextval' from 'auth_table_id_seq');
         btrim       
   ------------------
    uth_table_id_seq
   
   Is expected result. Probably you need some other string manipulation function. 
   
   regards, Sergei
   
   
   
   

3. Re: BUG #17407: trim trims more than expected

   Alvaro Herrera <alvherre@alvh.no-ip.org> — 2022-02-16T15:12:38Z

   On 2022-Feb-16, PG Bug reporting form wrote:
   
   > Unexpected output
   > 
   > demo=# select trim ('nextval(''' from
   > substring('nextval(''auth_table_id_seq''::regclass)' from '%#"%_id_seq#"%'
   > for '#' ));
   >       btrim       
   > ------------------
   >  uth_table_id_seq
   
   Not a bug.  trim() receives a *set* of characters to remove, not a
   *substring* to remove, so the 'a' in 'auth' is matched to the 'a' in
   'nextval(' and gets removed.
   
   You can probably achieve what you want by combining substring() with
   position() and char_length(), or by using a regular expression in
   regexp_replace().
   
   -- 
   Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
   "La conclusión que podemos sacar de esos estudios es que
   no podemos sacar ninguna conclusión de ellos" (Tanenbaum)