MySQL - replace first occurrence of string in column

replace_first_occurrence.sql

set @oldString = 'http://'; -- string to replace
set @newString = ''; -- string to replace with

UPDATE table_name
set column_name =
IF(
    INSTR(column_name, @oldString) <> 0,
    CONCAT(
        REPLACE(
            LEFT(column_name, INSTR(column_name, @oldString) - 1), @oldString, @newString
        ),
        SUBSTRING(column_name, INSTR(column_name, @oldString) + LENGTH(@oldString))
    ),
    column_name
);