How to Efficiently Count Rows in Your MySQL Queries?

Query Execution and Row Counting in MySQL

Counting the number of rows returned by a MySQL query is crucial for various database operations. This article provides comprehensive solutions for this task, catering to different scenarios and techniques.

Counting Total Rows in a Query Result

The simplest method to obtain the total number of rows is to iterate through the result and increment a counter. However, MySQL offers a built-in function, mysql_num_rows, which provides a direct count of the rows. For example, in PHP, you can use mysqli_num_rows as follows:

<code class="php"><?php
$result = mysqli_query($link, "SELECT * FROM table1");
$num_rows = mysqli_num_rows($result);
echo "$num_rows Rows\n";
?></code>

Counting Rows Matching Specific Criteria

To count rows that meet specific criteria, use the COUNT(*) function. For instance, to count rows where bar is equal to 'value':

SELECT COUNT(*) FROM foo WHERE bar= 'value';

Preserving Row Count with LIMIT

If you use the LIMIT clause but want to know the total number of rows without applying the limit, use SQL_CALC_FOUND_ROWS followed by SELECT FOUND_ROWS(). For example:

<code class="sql">SELECT SQL_CALC_FOUND_ROWS * FROM foo WHERE bar="value" LIMIT 10;
SELECT FOUND_ROWS();</code>

However, note that SQL_CALC_FOUND_ROWS is deprecated as of MySQL 8.0.17 and will be removed in later versions. It is recommended to use a separate query to calculate the count.

Best Practice for Large Tables

For large tables, running a separate query for counting can be inefficient. Instead, consider caching the count by executing a simpler query once and reusing it before launching more complex queries.

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