PDO::rowCount vs. COUNT(*) Performance

When counting rows in a database query, the choice between using PDO::rowCount and COUNT(*) can significantly impact performance.

PDO::rowCount

PDO::rowCount returns the number of rows affected by the last SQL statement. However, for SELECT statements, some databases may return the number of rows returned. This behavior is not guaranteed and should not be relied upon.

Internally, PDO::rowCount processes the entire result set, allocating memory for each row. This can be a memory-intensive operation, especially for large result sets.

COUNT(*)

COUNT() counts the number of rows in a query without retrieving the actual rows. MySQL optimizes COUNT() to find the count without fetching every row.

Performance Comparison

For performance reasons, COUNT() is generally faster than PDO::rowCount for counting rows. This is because COUNT() takes advantage of MySQL's optimization and avoids the memory-intensive operation of processing the entire result set.

Indexing

Using an index on the id column can significantly improve the performance of both methods. An index allows MySQL to quickly locate the rows matching the id value without having to scan the entire table.

Best Practice

Generally, it is recommended to use COUNT(*) instead of PDO::rowCount for counting rows in queries, especially when the result set is large. Additionally, using an index on the id column can further improve performance.