ORACLE - String Functions : rtrim

the rtrim function removes all specified characters from the right-hand side of a string.

The syntax is:

rtrim( string1, [ trim_string ] )

string1 is the string to trim the characters from the right-hand side.
trim_string is the string that will be removed from the right-hand side of string1. If this parameter is omitted, the rtrim function will remove all trailing spaces from string1.

For example:

rtrim('hola '); would return 'hola'
rtrim('hola ', ' '); would return 'hola'
rtrim('paris000', '0'); would return 'paris'
rtrim('332312paris1233213', '123'); would return '332312paris' (removes the individual occurrences of '1', '2', and '3')

ORACLE - String Functions : length

The length function returns the length of the specified string.

The syntax is:

length( string )

string is the string to return the length for.
If string1 is NULL, then the function returns NULL.

For example:

length('Hola Mundo') would return 10.
length('') would return NULL.

ORACLE - String Functions : Instr

The instr function returns the location of a substring in a string.
The syntax is:
instr( stringA, stringB [, start_position [, nth_appearance ] ] )
stringA is the string to search.
stringB is the substring to search for in stringA .
start_position is the position in stringA where the search will start. This argument is optional. If omitted, it defaults to 1. The first position in the string is 1. If the start_position is negative, the function counts back start_position number of characters from the end of stringA and then searches towards the beginning of stringA .
nth_appearance is the nth appearance of stringB. This is optional. If omitted, it defaults to 1.

For example:
instr('hello word hello', 'e') would return 2; the first occurrence of 'e'
instr('hello word hello', 'e', 1, 1) would return 2; the first occurrence of 'e'
instr('hello word hello', 'e', 1, 2) would return 13; the second occurrence of 'e'
instr('hello word hello', 'e', -3, 2) would return 2.
instr('hello word hello', 'X', 1, 1) would return 0.

ORACLE - Conversion Functions : To_char

the to_char function converts a number or date to a string.

The syntax :
to_char( value, [ format_mask ], [ nls_language ] )
value can either be a number or date that will be converted to a string.
format_mask is optional. This is the format that will be used to convert value to a string.
nls_language is optional. This is the nls language used to convert value to a string.

Examples - Numbers
The following are number examples for the to_char function.
to_char(1113214.23, '9999.999.9') would return '1113,214.7'
to_char(3214.23, '9,999.99') would return '3,214.23'
to_char(3214.23, '$9,999.00') would return '$3,214.23'
to_char(78, '000099') would return '000078'

Examples - Dates
The following are date examples for the to_char function.
to_char(sysdate, 'yyyy/mm/dd'); would return '2008/07/19'
to_char(sysdate, 'Month DD, YYYY'); would return 'July 19, 2003'