MySQL/MariaDB UDF functions implemented in C

Features:

• General Levenshtein algorithm
• k-bounded Levenshtein distance algorithm (linear time, constant space).
  • Info: this is when you only care about the distance if it's smaller or equal than your given k (e.g. to test if the spelling difference between two words is of maximum 1). In this case, the algorithm runs faster while using less memory.
• Levenshtein ratio
  • Info: this is syntactic sugar for levenshtein_ratio(s, t) = 1 - levenshtein(s, t) / max(s.length, t.length))
• k-bounded Levenshtein ratio

Install

First you need to compile the library and tell MySQL/MariaDB about it:

# Unix; on Linux x64 you may need to add the -fPIC flag
gcc -o levenshtein.so -shared levenshtein.c `mysql_config --include`  

# macOS
gcc -bundle -o levenshtein.so levenshtein.c `mysql_config --include`

# all systems
cp levenshtein.so `mysql_config --plugindir` # You may need sudo

If you run into issues, please take a look at this workaround or this.

Then in a console, run:

CREATE FUNCTION levenshtein RETURNS INT SONAME 'levenshtein.so';
CREATE FUNCTION levenshtein_k RETURNS INT SONAME 'levenshtein.so';
CREATE FUNCTION levenshtein_ratio RETURNS REAL SONAME 'levenshtein.so';
CREATE FUNCTION levenshtein_k_ratio RETURNS REAL SONAME 'levenshtein.so';

That should be all 🐬 ᵒᴥᵒᶅ !

Note

Just in case the last SQL statements failed, consider that to create and use UDF functions, you need CREATE ROUTINE, EXECUTE privileges.

For MariaDB you have to grant additional privileges on mysql database. Here is an example of privileges allowing dropping, altering, creating and using functions:

GRANT INSERT, DELETE, DROP ROUTINE, CREATE ROUTINE, ALTER ROUTINE, EXECUTE ON mysql.* TO 'user'@'%';

For more details on setting up UDFs in MySQL see: UDF Compiling and Installing

Run

For example:

select 3 = levenshtein('maneuver', 'manoeuvre');
select 3 = levenshtein_k('maneuver', 'manoeuvre', 5);  -- k=5, allow the distance to be up to 5, otherwise it's 6 or greater
select 2 = levenshtein_k('maneuver', 'manoeuvre', 1);  -- k=1, allow the distance to be up to 1, otherwise it's 2 or greater

select 0.6666666666666667 = levenshtein_ratio('maneuver', 'manoeuvre'); -- that is, 1 - 3/9
select 0.6666666666666667 = levenshtein_k_ratio('maneuver', 'manoeuvre', 5); -- same
select 0 = levenshtein_k_ratio('maneuver', 'manoeuvre', 1); -- 0 because the distance (3) is greater than the maximum k allowed (1)

Test (for Development)

Your contributions are very much welcome!

Please before making a pull request, run the unit tests file.

This should return 1 at the end:

mysql -uroot < unittest.sql  # Change your username & password as needed