MySQL

Case Insensitive REPLACE() for MySQL

One request I occasionally see is for a case insensitive version of REPLACE() for MySQL. I wrote this a while back, but here it is now for all of you to play around with. It uses a basic naïve string search algorithm, so can be slow under some circumstances.

DELIMITER $$

DROP FUNCTION IF EXISTS `replace_ci`$$
CREATE FUNCTION `replace_ci` ( str TEXT,needle CHAR(255),str_rep CHAR(255))
    RETURNS TEXT
    DETERMINISTIC
    BEGIN
        DECLARE return_str TEXT DEFAULT '';
        DECLARE lower_str TEXT;
        DECLARE lower_needle TEXT;
        DECLARE pos INT DEFAULT 1;
        DECLARE old_pos INT DEFAULT 1;

        SELECT lower(str) INTO lower_str;
        SELECT lower(needle) INTO lower_needle;
        SELECT locate(lower_needle, lower_str, pos) INTO pos;
        WHILE pos > 0 DO
            SELECT concat(return_str, substr(str, old_pos, pos-old_pos), str_rep) INTO return_str;
            SELECT pos + char_length(needle) INTO pos;
            SELECT pos INTO old_pos;
            SELECT locate(lower_needle, lower_str, pos) INTO pos;
        END WHILE;
        SELECT concat(return_str, substr(str, old_pos, char_length(str))) INTO return_str;
        RETURN return_str;
END$$

DELIMITER ;

SELECT replace_ci( 'mySQL', 'M', 'M' );

It’s also available on MySQL Forge.

Standard

5 thoughts on “Case Insensitive REPLACE() for MySQL

  1. Great post! I found a bug you may want to fix. If you’re using strings with spaces on both sides, it seems that when you declare the variables as CHAR() it truncates the last space! For example, try this:

    select replace_ci(‘ Cole Hayboy ‘, ‘ CO ‘, ”) from dual;

    There are spaces on both sides of the str and needle. The output should be the same as the input with no replacements, because of the trailing space in the needle. However, because the trailing space of the ‘ CO ‘ needle parameter is truncated, it finds a match and the output is “ole Hayboy “.

    If you change the data types for the needle and str_rep parameters to VARCHAR instead of CHAR, the function works as expected. It’s very bizarre, and may be an underlying MySQL bug. It took me forever to figure out why things were getting replaced that shouldn’t. I hope this helps someone else some day. :-D

  2. This works well. But I am looking for a function that will replace & maintain the case. For e.g. colour should be replaced with color & Colour with Color. Is this possible? Can anyone help?

Leave a Reply