How Can I Efficiently Calculate Total Results in MySQL Queries with Offset and Limit?

How to Determine Total Results with Offset and Limit in MySQL Queries

In pagination scenarios using Codeigniter or similar PHP/MySQL frameworks, it becomes crucial to determine the total number of results in a table to calculate the total number of pages. While the standard method of running a second query without limit functionality appears computationally inefficient, there exists an alternative solution that optimizes this process.

Utilizing SQL_CALC_FOUND_ROWS

MySQL provides a special function known as SQL_CALC_FOUND_ROWS. By including this statement before a query with limit and offset clauses, the database ensures that the total number of rows that would have been returned without limit is stored in a special internal variable. This allows for efficient retrieval of the total count without the need for an additional query.

For example, the following query includes SQL_CALC_FOUND_ROWS:

SELECT * FROM my_table WHERE category_id = ? ORDER BY id LIMIT 10 OFFSET 20

To retrieve the total count, simply execute the following query:

SELECT FOUND_ROWS()

This will return the total number of rows in the table that satisfy the where clause, regardless of the offset or limit parameters. By dividing this value by the limit value, you can obtain the total number of pages required for pagination.

By employing SQL_CALC_FOUND_ROWS, pagination becomes more efficient by eliminating the need for multiple database calls and ensuring accurate calculations for the total number of pages.

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