Crossfade two ore more strings in MySQL or MariaDB - mysql

Question

I'm looking for a lean way of overlapping/crossfading two or more strings in MySQL or MariaDB.
There is a base string like this:
XXXOOOOOOOXXX
Then there are n strings that need to crossfade that base string. The rule in this demo case is that X should be priority. The strings can be of different length.
So this strings overlapping the base string:
OOOOOXOOOOOOOOOX
XXOOOXXOOOOOXXXXO
should result in:
XXXOOXXOOOXXXXXXO
I could do this in PHP, but maybe there is a function inside MySQL or MariaDB that makes it faster.

Answer 1

There is not a function in MySQL which does do that, but one can be created:
CREATE DEFINER=`root`#`localhost` FUNCTION `crossfade`(
a VARCHAR(100),
b VARCHAR(100)) RETURNS varchar(100) CHARSET utf8mb4
BEGIN
DECLARE i INTEGER DEFAULT 1;
DECLARE r VARCHAR(100) DEFAULT '';
-- Make input equally long
IF LENGTH(a) < LENGTH(b) THEN
SET A = RPAD(A,LENGTH(b),' ');
ELSE
SET B = RPAD(B,LENGTH(a),' ');
END IF;
WHILE i<=LENGTH(a) DO
IF substring(a,i,1)='X' THEN
SET r = concat(r,substring(a,i,1));
ELSE
SET r = concat(r,substring(b,i,1));
END IF;
SET i = i + 1;
END WHILE;
RETURN r;
END
Example:
SELECT crossfade('OOOOOXOOOOOOOOOX','XXOOOXXOOOOOXXXXO');
output:
+ ------------------------------------------------------ +
| crossfade('OOOOOXOOOOOOOOOX','XXOOOXXOOOOOXXXXO') |
+ ------------------------------------------------------ +
| XXOOOXXOOOOOXXXXO |
+ ------------------------------------------------------ +