How to create custom functions in SQLite

You can write arbitrary functions in SQL with the define extension:

-- define a function to sum the numbers 1..n
select define('sumn', ':n * (:n + 1) / 2');

-- use it as a regular function
select sumn(3);
6
select sumn(5);
15

SQLite does not have a stored function/stored procedure language. So CREATE FUNCTION does not work. What you can do though is map functions from a c library to SQL functions (user-defined functions). To do that, use SQLite's C API (see: http://www.sqlite.org/c3ref/create_function.html)

If you're not using the C API, your wrapper API may define something that allows you access to this feature, see for example:

  • PHP sqlite_create_function() (http://www.php.net/manual/en/function.sqlite-create-function.php)
  • Python sqlite3.create_function() (http://docs.python.org/3/library/sqlite3.html#sqlite3.Connection.create_function)
  • Perl $dbh->sqlite_create_function($name,$argc,$code_ref,$flags) (https://metacpan.org/pod/DBD::SQLite#$dbh-%3Esqlite_create_function(-$name,-$argc,-$code_ref,-$flags-))

This could be useful to many: in SQLiteStudio it is possible to define new functions and collations easily from interface through a sql built-in plugin for example.

https://github.com/pawelsalawa/sqlitestudio/wiki/Official_plugins#sql-built-in

Through the function editor.

Tags:

Sqlite

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