class SQLiteDatabase { bool createFunction ( string function_name, callback callback [, int num_args] ) }
sqlite_create_function() allows you to register a PHP
function with SQLite as an UDF (User Defined
Function), so that it can be called from within your SQL statements.
The UDF can be used in any SQL statement that can call functions, such as
SELECT and UPDATE statements and also in triggers.
Parameters
dbhandle
The SQLite Database resource; returned from sqlite_open
() when used procedurally. This parameter is not required
when using the object-oriented method.
function_name
The name of the function used in SQL statements.
callback
Callback function to handle the defined SQL function.
Note:
Callback functions should return a type understood by SQLite (i.e.
scalar type).
num_args
Hint to the SQLite parser if the callback function accepts a
predetermined number of arguments.
Note: Two alternative syntaxes are
supported for compatibility with other database extensions (such as MySQL).
The preferred form is the first, where the dbhandle
parameter is the first parameter to the function.
Examples
Example 1. sqlite_create_function() example
<?php function md5_and_reverse($string) { return strrev(md5($string)); }
if ($dbhandle = sqlite_open('mysqlitedb', 0666, $sqliteerror)) {
In this example, we have a function that calculates the md5 sum of a
string, and then reverses it. When the SQL statement executes, it
returns the value of the filename transformed by our function. The data
returned in $rows contains the processed result.
The beauty of this technique is that you do not need to process the
result using a foreach() loop after you have queried for the data.
PHP registers a special function named php when the
database is first opened. The php function can be used to call any PHP
function without having to register it first.
Example 2. Example of using the PHP function
<?php $rows = sqlite_array_query($dbhandle, "SELECT php('md5', filename) from files"); ?>
This example will call the md5() on each
filename column in the database and return the result
into $rows
Note:
For performance reasons, PHP will not automatically encode/decode binary
data passed to and from your UDF's. You need to manually encode/decode
the parameters and return values if you need to process binary data in
this way. Take a look at sqlite_udf_encode_binary()
and sqlite_udf_decode_binary() for more details.
Tip:
It is not recommended to use UDF's to handle processing of
binary data, unless high performance is not a key requirement of your
application.
Tip:
You can use sqlite_create_function() and
sqlite_create_aggregate() to override SQLite native
SQL functions.
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