PDO::rowCount() vs. COUNT(*): What\'s the Best Method for Counting Rows in PDO?

PDO::rowCount() vs COUNT(*)

Introduction

When working with SQL databases using PDO, you come across two common methods for counting rows in a result set: PDO::rowCount() and COUNT(*). This article compares their performance, considering both indexed and non-indexed queries.

1st Question: Performance Comparison

• PDO::rowCount():

  • Server processes the entire result set, allocating memory for all results and entering fetching mode, which can be more resource-intensive.
  • Returns the number of rows affected by the last statement (may not always be accurate for SELECT statements).

• COUNT():

  • Server only allocates memory to store the result of the count.
  • Performs faster as it does not fetch all rows, especially when working with large tables.

Conclusion: COUNT() is generally faster for counting rows.

2nd Question: Index Optimization

When an index is set on a column, it significantly improves the performance of queries that involve that column.

• COUNT(id) vs COUNT(*) with Index:

  • COUNT(id) is preferred since it only counts rows where the id column is not null, yielding more accurate results.
  • COUNT(*) counts all rows, including those with null id values, which may not be desired in some cases.

Recommendation:

Use COUNT() for counting rows, and use COUNT(id) when working with indexed id columns to obtain more precise results.

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