1. CS122B: Projects in Databases and Web Applications Winter 2019
Professor Chen Li
Department of Computer Science
UC Irvine
Notes 12: User-Defined Functions (UDF) in MySQL

2. Purpose SQL has its own limitations
Enhance DB using functions implemented in C

3. Example: edit distance
Edit distance between two strings is the minimum number of single-character operations (insert/delete/substitute) to transform one to the other
Also known as Levenshtein distance
Example: ed(”schwazeneger”, ”schwarzenegger”) = 2

4. Dynamic programming for edit distance

5. Example
ed(”elephant”, ”relevant”) = 3

6. Supporting Edit Distance as UDF
Compile
Edit distance Function in C: ed.c
Shared library libed.so
CREATE FUNCTION ed RETURNS INTEGER SONAME 'libed.so';
SELECT ed('abc', 'ad');
MySQL

7. Example: using ed as a UDF
select * from stars where name = ’Arnold schwarzenegger' limit 5
select * from stars where ed(name, 'Arnold Schwarzeneger') <= 2 limit 5