Efficient Algorithm for String Concatenation with Overlap

Question

We need to combine 3 columns in a database by concatenation. However, the 3 columns may contain overlapping parts and the parts should not be duplicated. For example,

<

Answer 1

Or you could do it in mysql with the following stored function:

DELIMITER //

DROP FUNCTION IF EXISTS concat_with_overlap //

CREATE FUNCTION concat_with_overlap(a VARCHAR(100), b VARCHAR(100))
  RETURNS VARCHAR(200) DETERMINISTIC
BEGIN 
  DECLARE i INT;
  DECLARE al INT;
  DECLARE bl INT;
  SET al = LENGTH(a);
  SET bl = LENGTH(a);
  IF al=0 THEN 
    RETURN b;
  END IF;
  IF bl=0 THEN 
    RETURN a;
  END IF;
  IF al < bl THEN
     SET i = al;
  ELSE
     SET i = bl;
  END IF;

  search: WHILE i > 0 DO
     IF RIGHT(a,i) = LEFT(b,i) THEN
    RETURN CONCAT(a, SUBSTR(b,i+1));
     END IF;
     SET i = i - 1;
  END WHILE search;

  RETURN CONCAT(a,b);
END//

I tried it with your test data:

mysql> select a,b,c,
    -> concat_with_overlap( concat_with_overlap( a, b ), c ) as result 
    -> from testing //
+-------------+---------+--------+-------------+
| a           | b       | c      | result      |
+-------------+---------+--------+-------------+
| a           | b       | c      | abc         |
| abcde       | defgh   | ghlmn  | abcdefghlmn |
| abcdede     | dedefgh |        | abcdedefgh  |
| abcde       | d       | ghlmn  | abcdedghlmn |
| abcdef      |         | defghl | abcdefghl   |
| abXabXabXac | XabXac  |        | abXabXabXac |
+-------------+---------+--------+-------------+
6 rows in set (0.00 sec)