Re: The same result for with SPACE and without SPACE

Hi David,
I appreciate your response.

I did the analysis.
It sounds me that in realistic scenario, CHAR_10 and VAR_CHAR_10 columns with the same data will fetch the desired results. It sounds me that there is no conflict.

select

length( '123'::char(5)),

length( '123 '::char(5)),

length('123'::varchar),

length('123 '::varchar),

length(('123 '::char(5))::varchar),

'123 '::char(5) = '123 '::varchar,

('123 '::char(5))::varchar = '123 '::varchar --- this is FALSE which is fine because VARCHAR is not padding the space.

;

Output:-

3 3 3 7 3 true false

Thanks,
Sarwar

________________________________
From: David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
Sent: Thursday, June 15, 2023 2:04 PM
To: M Sarwar <sarwarmd02(at)outlook(dot)com>
Cc: Scott Ribe <scott_ribe(at)elevated-dev(dot)com>; Wetmore, Matthew (CTR) <Matthew(dot)Wetmore(at)express-scripts(dot)com>; mahesh <mahesha_dba(at)yahoo(dot)com>; Mohammed Aslam <hmdaslam97(at)gmail(dot)com>; pgsql-admin(at)lists(dot)postgresql(dot)org <pgsql-admin(at)lists(dot)postgresql(dot)org>; Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: The same result for with SPACE and without SPACE

On Thu, Jun 15, 2023 at 10:44 AM M Sarwar <sarwarmd02(at)outlook(dot)com<mailto:sarwarmd02(at)outlook(dot)com>> wrote:
Hello Scott and all,

Here the question comes with respect to CHAR(10) to CHARACTeR VARYING( 10 ) comparison results.
char_10 - type character ( 10 )
var_char_10 - type character varying ( 10)

When I do the comparison between char_10 and var_char_10 columns, I may get the wrong results.
var_char_10 is always trimmed from right.

NO. varchar is never trimmed in this sense. Though casting to a varchar(n) will result in truncation of the input value to n characters - regardless of what those characters are.

char_10 has padded data of blank or spaces.
Now I compare char10 and var_char_10 columns, I will get the wrong results because char_10 has padded spaces.

Is that correct or will it ignore whitespaces at the end of char_10 column?

Testing shows that the varchar value gets promoted to char, not the other way around.

postgres=# select '123 '::char(5) = '123 '::varchar;
?column?
----------
t
(1 row)

postgres=# select ('123 '::char(5))::varchar = '123 '::varchar;
?column?
----------
f
(1 row)

No one memorizes char behavior - if you must use it then test your code, and maybe be extra explicit with your casting too.

David J.