The INITCAP function converts the case of a string so that each word starts with a capital letter and all subsequent letters are in lowercase.

SELECT INITCAP('HELLO mr macdonald!') AS NEW FROM dual;

Output

NEW
-------------------
Hello Mr Macdonald!

The Oracle SQL and PL/SQL || operator allows you to concatenate 2 or more strings together.

Example:

Assuming the following customers table:

id  firstname    lastname
---  -----------  ----------
  1  Thomas       Woody

Query:

SELECT firstname || ' ' || lastname || ' is in my database.' as "My Sentence" 
   FROM customers;

Output:

My Sentence
---------------------------------
Thomas Woody is in my database.

Oracle also supports the standard SQL CONCAT(str1, str2) function:

Example:

Query:

SELECT CONCAT(firstname, ' is in my database.') from customers;

Output:

Expr1
---------------------------------
Thomas is in my database.

The UPPER function allows you to convert all lowercase letters in a string to uppercase.

SELECT UPPER('My text 123!') AS result FROM dual;

Output:

RESULT    
------------
MY TEXT 123!

LOWER converts all uppercase letters in a string to lowercase.

SELECT LOWER('HELLO World123!') text FROM dual;

Outputs:

Let's say we want to replace only numbers with 2 digits: regular expression will find them with (\d\d)

SELECT REGEXP_REPLACE ('2, 5, and 10 are numbers in this example', '(\d\d)', '#')
FROM dual;

Results in:

'2, 5, and # are numbers in this example'

If I want to swap parts of the text, I use \1, \2, \3 to call for the matched strings:

SELECT REGEXP_REPLACE ('swap around 10 in that one ', '(.*)(\d\d )(.*)', '\3\2\1\3')
 FROM dual;

SUBSTR retrieves part of a string by indicating the starting position and the number of characters to extract

SELECT SUBSTR('abcdefg',2,3) FROM DUAL;

returns:

bcd

To count from the end of the string, SUBSTR accepts a negative number as the second parameter, e.g.

SELECT SUBSTR('abcdefg',-4,2) FROM DUAL;

returns:

de

To get the last character in a string: SUBSTR(mystring,-1,1)

LTRIM and RTRIM remove characters from the beginning or the end (respectively) of a string. A set of one or more characters may be supplied (default is a space) to remove.

For example,

select LTRIM('<===>HELLO<===>', '=<>')
      ,RTRIM('<===>HELLO<===>', '=<>')
from dual;

Returns:

HELLO<===>
<===>HELLO