Oracle trim function usage

I read the Oracle document today and found that trim function usage is not limited to removing spaces of strings! Read the official explanation and the following experiment. I hope you can learn it together!

1. first look at the trim function syntax diagram: http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions199.htm

The syntax is described as follows:

TRIM ([{LEADING | TRAILING | BOTH}
[Trim_character]
| Trim_character
}
FROM
]
Trim_source
) Parameter explanation:

Leading

Trailing end character

Both start and end characters

Characters removed by trim_character

Trim_source trim Source

2. The following functions are introduced:

The trim function is used to remove the start or end (or both) characters of a string.

1) if the leading parameter is specified, the oracle database removes any starting characters equal to trim_character.

Example:

SQL> select trim (leading 'X' from 'xdylan') "test_trim" from dual;

Test_trim
--------------------
Dylan

2) If the traling parameter is specified, oracle removes any trailing characters equal to trim_character.

Example:

SQL> select trim (trailing 'X' from 'dylanx') "test_trim" from dual;

Test_trim
--------------------
Dylan

3) if the both parameter is specified or none of the three parameters are specified, oracle removes any starting and ending characters equal to trim_character.

Example:

SQL> select trim (both 'X' from 'xdylanx') "test_trim" from dual;

Test_trim
--------------------
Dylan

SQL> select trim ('x' from 'xdylanx') "test_trim" from dual;

Test_trim
--------------------
Dylan

4) if the trim_character parameter is not specified, spaces are removed by default.

Example:

SQL> select trim (both from 'dylan') "test_trim" from dual;

Test_trim
--------------------
Dylan

5) If you only specify the trim source (trim_source), oracle removes spaces at the beginning and end of trim_source.

Example:

SQL> select trim ('dylan') "test_trim" from dual;

Test_trim
--------------------
Dylan

6) The trim function returns a value of the varchar2 type. The maximum length of this value is equal to the length of trim_source.

7) If either trim_source or trim_character is null, the trim function returns null.

Example:

SQL> select trim (trailing null from 'dylan') "test_trim" from dual;

Test_trim
--------------------

 

SQL> select trim (trailing 'X' from null) "test_trim" from dual;

Test_trim
--------------------

Note: Both trim_character and trim_source can belong to any of the following data types: CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or nclob.

The type of the returned value is the same as that of trim_source. The following is an official example: retrieve records with employment dates not starting with 0 in the employees table.

SELECT employee_id,
TO_CHAR (TRIM (LEADING 0 FROM hire_date ))
FROM employees
WHERE department_id = 60;

EMPLOYEE_ID TO_CHAR (T
--------------------
103 3-JAN-90
104 21-MAY-91
105 25-JUN-97
106 5-FEB-98
107 7-FEB-99