Note: If the function parameter is not surrounded by

quotation marks

, then the parameter is going to be interpreted as a column value. Converts a string or column value to

UPPER-CASE

SELECT 
    UPPER(first_name), 
    UPPER('Converts a string or column value to UPPER-CASE') 
FROM students

Converts a string or column value to

lower-case

SELECT 
    LOWER(first_name), 
    LOWER('Converts a string or column value to lower-case') 
FROM students

Joins strings and columns together

SELECT 
    CONCAT(first_name, ' ', 'joins', ' ', 'strings', ' ', 'and', ' ', 'columns') 
FROM students

The function

LENGTH

Returns the length (in bytes)

SELECT 
    id, 
    first_name,
    LENGTH(first_name) first_name_length 
FROM students

Note: Each Georgian letter takes

three bytes

The function is similar to

CONCAT

where

WS

means - With Separator. The first parameter is the separator between each one of the additional fields, that we pass as next parameters

SELECT 
    CONCAT_WS(' - ', first_name, 'joins', 'strings', 'and', 'columns', 'with', 'separator') 
FROM students

The function

TRIM

removes leading and trailing spaces

SELECT 
    LENGTH(' text ') length,
    LENGTH(TRIM(' text ')) length_with_trim

The function

RTRIM

removes trailing spaces (removes spaces from the end)

SELECT 
    LENGTH(' text ') length,
    LENGTH(RTRIM(' text ')) length_with_right_trim

The function

LTRIM

remove leading spaces (removes spaces from the beginning)

SELECT 
    LENGTH(' text ') length,
    LENGTH(LTRIM(' text ')) length_with_left_trim

The function

LEFT

returns leftmost characters. In this case 5 characters because we pass 5 as second parameter

SELECT 
    LEFT(first_name, 5) AS 'five leftmost characters'
FROM students

The function

RPAD

appends string (third parameter) the specified number of times (second parameter) to the first parameter. In this example each one of the student's last name that is less than 10 characters long, is filled with

-

SELECT 
    RPAD(first_name, 10, '-') AS 'student name'
FROM students

Complete list of string functions on the official documentation: https://dev.mysql.com/doc/refman/8.0/en/string-functions.html