why we are using fm and trim in char functions [closed] - sql

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Query #1
Select *
from EMPLOYEE
where trim( to_char(joining_date,'Month')) ='January';
Query#2
select *
from employee
where to_char(joining_date,'Month')='January';
Query #3
select *
from employee
where to_char(joining_date,'fmMonth')='January';
If I do first query I am getting answer.
If I do 2nd query I am not getting answer .
If I use fm in 3rd query I am getting answer
What is the reason behind this.

Answer 1

Cause Oracle (I guess you're working with Oracle) adds blank spaces (padding) so that the results have always the same "size" (format) when formatting values.
Fake example, without trim or fm (oh, how nicely formatted is this !)
01 January 2015
12 September 2015
With Fm version or trim, you remove these "padding" spaces.
Fake example, with trim or fm (oh, that's ugly, but at least I don't have all these spaces)
1 January 2015
12 September 2015

Answer 2

With FM (stands for format mask) prefix, you are applying the format_mask. This means that you are asking query engine that zeros and blanks are meant to be suppressed.
If you are asking why trim or FM then you should try running these two queries to understand it:
select length(trim(to_char(to_date('15052015', 'DDMMYYYY'), 'MONTH'))) from dual;
select length(to_char(to_date('15052015', 'DDMMYYYY'), 'MONTH')) from dual;
select length(trim(to_char(to_date('15092015', 'DDMMYYYY'), 'MONTH'))) from dual;
select length(to_char(to_date('15092015', 'DDMMYYYY'), 'MONTH')) from dual;
Since your NLS setting by default for NLS_DATE_LANGUAGE would be ENGLISH, May takes 3 characters while September takes 9 characters. Hence by default it will add 6 additional characters to May as well.

Answer 3

The FM amodifier, used in format models in the TO_CHAR function, control blank padding and exact format checking.
The SQL TRIM() removes leading and trailing characters(or both) from a character string.