PHP Pdo\Sqlite::createAggregate() Method: Usage and Examples

Registers a PHP step callback and finalizer as an SQLite aggregate function.

The objective is to understand the behavior and operational limits, not only the method name.

What It Does

Registers a PHP step callback and finalizer as an SQLite aggregate function.

Syntax and Return Value

Pdo\Sqlite::createAggregate(...)

The return value and exceptional cases depend on the call described here: The step callback receives an accumulator and row number; return scalar output from finalization.

Requirements: install and enable the corresponding PHP driver or extension and configure the service before running the examples.

The driver-specific PDO subclasses are available starting with PHP 8.4, except setAuthorizer, which starts with PHP 8.5.

Example 1: Basic Use

The step callback accumulates state from each row; the finalizer returns one scalar SQL result.

<?php
$sqlite = PDO::connect("sqlite::memory:");
$sqlite->exec("CREATE TABLE scores (name TEXT, points INTEGER)");
$sqlite->exec("INSERT INTO scores VALUES ('Ava',10),('Ben',20),('Cai',30)");
$sqlite->createAggregate("sum_bonus",
    static fn($total, int $row, $points) => ($total ?? 0) + (int) $points + 1,
    static fn($total, int $rows) => (int) ($total ?? 0),
    1
);
echo $sqlite->query("SELECT sum_bonus(points) FROM scores")->fetchColumn();

Example 2: A Second Scenario

The step callback accumulates state from each row; the finalizer returns one scalar SQL result.

<?php
$sqlite = PDO::connect("sqlite::memory:");
$sqlite->exec("CREATE TABLE scores (name TEXT, points INTEGER)");
$sqlite->exec("INSERT INTO scores VALUES ('Ava',10),('Ben',20),('Cai',30)");
$sqlite->createAggregate("sum_bonus",
    static fn($total, int $row, $points) => ($total ?? 0) + (int) $points + 2,
    static fn($total, int $rows) => (int) ($total ?? 0),
    1
);
echo $sqlite->query("SELECT sum_bonus(points) FROM scores")->fetchColumn();

Example 3: Practical Checks

The step callback accumulates state from each row; the finalizer returns one scalar SQL result.

<?php
$sqlite = PDO::connect("sqlite::memory:");
$sqlite->exec("CREATE TABLE scores (name TEXT, points INTEGER)");
$sqlite->exec("INSERT INTO scores VALUES ('Ava',10),('Ben',20),('Cai',30)");
$sqlite->createAggregate("sum_bonus",
    static fn($total, int $row, $points) => ($total ?? 0) + (int) $points + 3,
    static fn($total, int $rows) => (int) ($total ?? 0),
    1
);
echo $sqlite->query("SELECT sum_bonus(points) FROM scores")->fetchColumn();

Important Behavior and Edge Cases

The step callback receives an accumulator and row number; return scalar output from finalization.

For production use, also account for error handling, data validation, resource limits and environment-specific driver behavior.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Registers a PHP step callback and finalizer as an SQLite aggregate function.
• The step callback receives an accumulator and row number; return scalar output from finalization.
• createFunction registers a scalar function executed once per matching SQL invocation.

Choose this API or pattern when its exact semantics match your task, and verify the result against the database driver and runtime used by your application.