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PL/php -- PHP Procedural Language for PostgreSQL

User documentation
07/12/2010

What is PL/php?

PL/php is a procedural language with hooks into the PostgreSQL database sytem, intended to allow writing of PHP functions for use as functions inside the PostgreSQL database. It was written by Command Prompt, Inc. and has since been open sourced and licensed under the PHP and PostgreSQL (BSD) licenses.

Download and Installation

Please see the installation documentation.

Creating the PL/php language

Please see the documentation on how to create the language in a database once the library is installed.

Functions and Arguments

To create a function, use the standard syntax:

CREATE FUNCTION funcname (argument-types) RETURNS return-type AS $$
   # plphp function body here
$$ LANGUAGE 'plphp';

Arguments are passed in the $args array and the result value is returned with the 'return' statement.

CREATE FUNCTION plphp_max(integer, integer) RETURNS integer AS $$
   if ($args[0] > $args[1]) {
      return $args[0];
   } else {
      return $args[1];
   }     
$$ STRICT LANGUAGE 'plphp'

NOTE: The use of the STRICT clause saves us from having to
think about NULL input values to our function. In a STRICT function,
when a NULL value is passed, the function will not be run at all,
but the system will just return a NULL result automatically.

In a non-strict function, if the actual value of an argument is NULL,
the corresponding $args[n-1] variable will be unset.

Data Types and Returns

The arguments passed into your PL/php function are converted to text so you can manipulate them with the loose typing enjoyed in typical PHP scripts. Conversely, the return command will accept any string that is acceptable input format for the function's declared return type.

Global Shared Variable

There is a global variable that can be used to store data between function calls, called $_SHARED.

CREATE FUNCTION set_var(text) RETURNS text AS $$
   global $_SHARED;
   $_SHARED['first']=$args[0];
   return 'ok';
$$ LANGUAGE 'plphp';

CREATE FUNCTION get_var() RETURNS text AS $$
   global $_SHARED;
   return $_SHARED['first'];
$$ LANGUAGE 'plphp';

SELECT set_var('hello plphp');
SELECT get_var(); -- will return 'hello plphp'

NOTE: The shared global variable is connection-specific. This is
useful for passing information around a single script execution,
but it is wiped when the connection is closed.

PostgreSQL Array Support

PL/php supports multi-dimensional arrays.

For example:

CREATE FUNCTION php_array() RETURNS text[][] AS $$
   $return = array(array("Steven", "Klassen"),
                   array("Jonathan", "Daugherty"));

   return $return;
$$ LANGUAGE 'plphp';

sklassen=# select php_array();
                php_array                
-----------------------------------------
 {{Steven,Klassen},{Jonathan,Daugherty}}
(1 row)

Polymorphic Arguments and Return Types

Functions may be declared to accept and return the polymorphic types 'anyelement', 'anyarray', and 'anyrecord'. See the PostgreSQL documentation for a more detailed explanation of polymorphic types: Polymorphic types

For example,

CREATE FUNCTION array_three_values(anyelement, anyelement, anyelement) RETURNS anyarray AS '
   $ret[0] = $args[0];
   $ret[1] = $args[1];
   $ret[2] = $args[2];
   return $ret;
' LANGUAGE 'plphp';

SELECT array_three_values(3,2,1);
 array_three_values
--------------------
 {3,2,1}
(1 row)

CREATE OR REPLACE FUNCTION php_row(integer) RETURNS record AS '
   $ret[f1]=$args[0];
   $ret[f2]="hello";
   $ret[f3]="world";
   return $ret;
' LANGUAGE 'plphp';

select * FROM php_row(1) AS (f1 integer, f2 text, f3 text);

Database Access (SPI)

The following functions are provided for database access.

  1. spi_exec - Execute a query with optional limit.
    resource spi_exec(string query[, int limit])
  2. spi_fetch_row - Return an associative array of the row's results.
    array spi_fetch_row(resource result)
  3. spi_status - Return the status of a previous query. If this is SPI_OK_SELECT you can obtain tuples from the result using spi_fetch_row.
    string spi_status(resource result)
  4. spi_processed - Return the number of tuples in a result.
    int spi_processed(resource result)
  5. spi_rewind - Put the row cursor at the beginning of the result, so spi_fetch_row will continue fetching tuples from the beginning of the result.
    void spi_rewind(resource result)

For example:

This isn't a particularly useful function, but it will illustrate the above-described access functions. You provide an integer id and it returns the username text field.

CREATE FUNCTION get_username(integer) RETURNS text AS $$
   # Assign the query to a variable.
   $query = "SELECT username FROM users WHERE id = " .$args[0];

   # Run the query and get the $result object.
   $result = spi_exec_query($query);

   # Fetch the row from the $result.
   $row = spi_fetch_row($result);

   return $row['username'];
$$ LANGUAGE 'plphp';

sklassen=# select get_username(1);
 get_username 
--------------
 sklassen
(1 row)

Note that results from spi_exec_query are allocated in RAM as a whole, so if you need to process huge result sets, you need to use a cursor. This is not possible with the current interface however, so if you need to do this, bug the developers.

Triggers

When a function is being used to return a trigger, the associative array $_TD contains trigger-related values.

  • $_TD[new]
    An associative array containing the values of the new table row for INSERT/UPDATE actions, or empty for DELETE. The array is indexed by field name. Note: Fields that are NULL will not appear in the array.
  • $_TD[old]
    An associative array containing the values of the old table row for UPDATE/DELETE actions, or empty for INSERT. The array is indexed by field name. Note: Fields that are NULL will not appear in the array.
  • $_TD[name]
    Contains the trigger name itself.
  • $_TD[event]
    Contains one of the values: "INSERT", "UPDATE", "DELETE".
  • $_TD[when]
    Contains one of the values: "BEFORE", "AFTER".
  • $_TD[level]
    Contains one of the values: "ROW", "STATEMENT".
  • $_TD[relid]
    Contains the relation ID of the table on which the trigger occured.
  • $_TD[relname]
    Contains the relation name.
  • $_TD[schemaname]
    Contains the schema name of the relation.
  • $_TD[args]
    An array of arguments passed to the trigger, if any. They can be accessed as $_TD["args"][idx].
  • $_TD[argc]
    The number of arguments passed to the trigger, 0 if none.

Example of an AFTER INSERT trigger

Suppose you have a users table with the typical columns and an activity table that you're using to track page accesses. On row INSERT to the activity table, you want to update the last_seen field of the appropriate user's record.

Consider the following table definitions:

CREATE TABLE users (
    id serial PRIMARY KEY NOT NULL,
    username text NOT NULL,
    email text,
    last_seen timestamp without time zone,
    active boolean DEFAULT true NOT NULL
);

CREATE TABLE activity (
    id serial PRIMARY KEY NOT NULL,
    users_id integer NOT NULL,
    file_accessed text NOT NULL,
    stamp timestamp without time zone DEFAULT now() NOT NULL,
    CONSTRAINT users_id_exists FOREIGN KEY (users_id) REFERENCES users(id)
);

CREATE FUNCTION update_lastseen() RETURNS trigger AS $$
    $new =& $_TD['new'];

    if (isset($new['users_id']) && isset($new['stamp'])) {
        $query = "UPDATE users SET last_seen = '" .$new['stamp'].
                 "' WHERE id = " .$new['users_id'];

        $rv = spi_exec($query);
    }

    return;
$$ LANGUAGE 'plphp';

CREATE TRIGGER after_update_lastseen_trigger
    AFTER INSERT ON activity FOR EACH ROW EXECUTE PROCEDURE update_lastseen();

1. insert a new user row.

sklassen=# insert into users (username, email) values ('sklassen','sklassen@commandprompt.com');
INSERT 1

sklassen=# select * from users where username = 'sklassen';

 id | username |           email            | last_seen | active 
----+----------+----------------------------+-----------+--------
  1 | sklassen | sklassen@commandprompt.com |           | t
(1 row)

2. Insert a new row into the activity table.

sklassen=# insert into activity (users_id, file_accessed) values (1,'index.html');
INSERT 1

3. Check and make sure the trigger fired as expected.

sklassen=# select * from users where username = 'sklassen';
 id | username |           email            |         last_seen          | active 
----+----------+----------------------------+----------------------------+--------
  1 | sklassen | sklassen@commandprompt.com | 2005-01-10 09:48:57.191595 | t
(1 row)

Example of a BEFORE INSERT OR UPDATE trigger

Let's say we have a user named admin that we want to prevent the application from modifying. We'll create a BEFORE DELETE trigger that prevents them from deleting the row and a BEFORE UPDATE trigger that prevents them modifying the username on which the previous trigger depends.

CREATE TABLE users (username text, email text);
INSERT INTO users VALUES ('admin', 'admin@commandprompt.com');
INSERT INTO users VALUES ('darcy', 'darcy@example.com');

CREATE OR REPLACE FUNCTION immortal() RETURNS trigger AS $$
   # The record may not be deleted if the username is "admin".
   if ($_TD['old']['username'] == 'admin') {
      pg_raise('notice', "You cannot delete the admin user");
      return 'SKIP';
   }
   return;
$$ LANGUAGE 'plphp';

CREATE TRIGGER before_delete_immortal_trigger BEFORE DELETE ON users
FOR EACH ROW EXECUTE PROCEDURE immortal();

CREATE OR REPLACE FUNCTION protect_admin() RETURNS trigger AS $$
   # Do not let them modify the username of the admin account.
   $oldUsername = $_TD['old']['username'];
   $newUsername = $_TD['new']['username'];

   if ($oldUsername == 'admin' && ($oldUsername != $newUsername)) {
      pg_raise('notice', "You cannot change the admin username.");
      return 'SKIP';
   } else {
      return;
   }
$$ LANGUAGE 'plphp';

CREATE TRIGGER before_update_protect_admin_trigger BEFORE UPDATE ON
users FOR EACH ROW EXECUTE PROCEDURE protect_admin();

Now the user admin cannot be deleted, nor its username can be changed:

pl_regression=# select * from users;
 username |          email          
----------+-------------------------
 admin    | admin@commandprompt.com
 darcy    | darcy@example.com
(2 rows)

pl_regression=# update users set username = 'foobar';
NOTICE:  plphp: You cannot change the admin username.
UPDATE 1

pl_regression=# select * from users;
 username |          email          
----------+-------------------------
 admin    | admin@commandprompt.com
 foobar   | darcy@example.com
(2 rows)

pl_regression=# delete from users;
NOTICE:  plphp: You cannot delete the admin user
DELETE 1

pl_regression=# select * from users;
 username |          email          
----------+-------------------------
 admin    | admin@commandprompt.com
(1 row)

Trusted vs. Untrusted

Normally, PL/php is installed as a "trusted" procedural language named 'plphp'. In this configuration, PHP will run in safe mode . Read more about the restrictions in the PHP documentation

In general, the operations that are restricted are those that interact with the environment. This includes file operations, require, and use (for external modules).

Since there is no way to gain access to the internals of the database backend process or the operating system itself, any unprivileged database user may use functions written in this language.

An example of a NON-working function due to security constraints:

CREATE FUNCTION read_passwd_file() RETURNS text AS '
   readfile("/etc/passwd");
   return 0;
' LANGUAGE 'plphp';

It will appear to execute, but depending on your log level, you'll may see something like the following:

Warning: readfile(): SAFE MODE Restriction in effect. The script
whose uid is 500 is not allowed to access /etc/passwd owned by uid 0
in Command line code on line 3

Warning: readfile(/etc/passwd): failed to open stream: Success in
plphp function source on line 3

Sometimes it is desirable to write PHP functions that are not restricted. In this case, you can create the language as 'plphpu' to enable the previously unavailable functions.

 CREATE LANGUAGE plphpu;

Composite Type Arguments

Composite-type arguments are passed to the function as associative array. The keys of the array are the attribute names of the composite type. Here is an example:

CREATE TABLE employee (
   name text,
   basesalary integer,
   bonus integer
);

CREATE FUNCTION empcomp(employee) RETURNS integer AS '
   return $args[0]["basesalary"] + $args[0]["bonus"];
' LANGUAGE 'plphp';

INSERT INTO employee values ('Josh', 1000, 10);
INSERT INTO employee values ('Darcy', 500, 20);

SELECT name, empcomp(employee) FROM employee;

This example results in the following output:

 name  | empcomp 
-------+---------
 Josh  |    1010
 Darcy |     520
(2 rows)

Returning A Row (composite type)

To return a row or composite-type value from a PL/php-language function, you can use an indexed array:

CREATE TYPE php_row AS (f1 integer, f2 text, f3 text);

CREATE OR REPLACE FUNCTION php_row(integer) RETURNS php_row AS $$
   $ret['f1'] = $args[0];
   $ret['f3'] = "world";
   $ret['f2'] = "hello";
   return $ret;
$$ LANGUAGE 'plphp';

SELECT * FROM php_row(1);

Will return:

 f1 |  f2   |  f3
----+-------+-------
  1 | hello | world

Returning multiple rows (SRF functions)

SRF stands for "set-returning functions". This means you can return multiple rows, like in the following example:

CREATE TYPE php_row AS (f1 integer, f2 text, f3 text);

CREATE OR REPLACE FUNCTION php_set(integer) RETURNS SETOF php_row AS $$
   $ret['f1'] = $args[0];
   $ret['f2'] = "hello";
   $ret['f3'] = "world";
   return_next($ret);

   $ret['f1'] = 2 * $args[0];
   $ret['f2'] = "hello";
   $ret['f3'] = "postgres";
   return_next($ret);

   $ret['f1'] = 3 * $args[0];
   $ret['f2'] = "hello";
   $ret['f3'] = "plphp";
   return_next($ret);
$$ LANGUAGE 'plphp';

This will result in:

pl_regression=# SELECT * FROM php_set(1);
 f1 |  f2   |    f3
----+-------+----------
  1 | hello | world
  2 | hello | postgres
  3 | hello | plphp
(3 rows)

The important thing to notice here is the return_next() function. This function must be called with a single parameter, which must be an array with one element per attribute of the return type. Note that currently the names of the array elements are ignored; the elements are assigned to attributes in order. If you must return a null value, asign a null value to an array element. This may be fixed in a future release.

Finishing a SRF is done by either calling return or by falling off the end of the function. At that point the entire results are delivered back to the outer query, be it directly to the user or to be joined to other tables/SRFs/etc.

The return tuples are written to a Postgres "tuplestore", which is disk-backed, and thus do not need to fit entirely in RAM.

Function Argument Names

You can assign names to pl/php function arguments:

CREATE FUNCTION plphp_match(document text, word text) RETURNS BOOL AS
$$
   if (strstr($document, $word))
       return TRUE;
   else
       return FALSE;
$$ LANGUAGE 'plphp';

Example output:

template1=# select plphp_match('PostgreSQL', 'SQL');
 plphp_match 
-------------
 t
(1 row)

Both $name and $args[position] variable access methods are supported.

Limitations

PL/php functions cannot call each other directly because their names are mangled.

SPI calls have the whole results allocated in memory, so processing huge results may be problematic. Also it's not possible to use cursors with SPI.

Files