How to Efficiently Count Rows Returned by a PHP PDO SELECT Query?

PHP PDO: Retrieving the Number of Rows Returned by a SELECT Query

Although PDO lacks a dedicated method for counting the rows returned by a SELECT query, several alternative approaches are available to achieve this functionality.

Using rowCount()

The PDOStatement class provides a rowCount() method that returns the number of rows affected by an UPDATE, INSERT, or DELETE statement. However, the manual advises against using rowCount() with SELECT statements, as it may not accurately reflect the row count.

Using a COUNT(*) Subquery

According to the PDO documentation, the recommended approach is to use a PDO::query() subquery with COUNT(*) to count the rows. The number of rows can then be retrieved using PDOStatement::fetchColumn(). For example:

$stmt = $conn->prepare('SELECT COUNT(*) FROM table');
$stmt->execute();
$rowCount = $stmt->fetchColumn();

Using Fetching Methods

If you have already fetched the data into a result set, you can use one of the fetch* methods to retrieve the data and use the count() function to determine the number of rows. For example, using the fetchAll() method:

$stmt = $conn->query('SELECT * FROM table');
$rows = $stmt->fetchAll();
$rowCount = count($rows);

Additional Considerations

When using a SELECT query with a LIMIT clause, the rowCount() method may return the row count before the LIMIT is applied. Therefore, it is generally recommended to use the subquery approach described above to ensure accuracy.

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