How Can I Efficiently Search for a Number in the Last N Rows of a Large MySQL Table?

Efficiently Searching for a Number in the Last N Rows of a Large MySQL Table

In a massive MySQL table with millions of rows, you may encounter the need to determine if a specific number appears in the last n rows. To do this efficiently, consider utilizing the following approach:

Starting with the concept proposed by @chaos, some crucial modifications enhance the query's performance:

• Explicit ORDER BY for LIMIT: Always specify ORDER BY in conjunction with LIMIT to ensure the order of the rows. Relying on implicit ordering can lead to inconsistent results and is not portable.
• Descending Order: By ordering in descending order, you eliminate the need to know the total number of rows in the table beforehand.
• Correlation Name for Derived Table: Assign a correlation name (table alias) to the derived table to distinguish it from the original table.

With these modifications in place, the optimized query becomes:

SELECT `id`
FROM (
    SELECT `id`, `val`
    FROM `big_table`
    ORDER BY `id` DESC
    LIMIT $n
) AS t
WHERE t.`val` = $certain_number;

This query efficiently searches for the occurrence of $certain_number within the last $n rows of the big_table, providing a fast and reliable solution for your data检索 needs.

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