How to Optimize MySQL Queries with Large Offsets in LIMIT Clause?

Optimizing MySQL Queries with Large Offset in LIMIT Clause

When executing a MySQL query with a significant offset in the LIMIT clause, performance issues may arise. This can be a challenge when traditional offset-based methods, such as SELECT * FROM table LIMIT m, n;, become inefficient for large offset values (e.g., over 1,000,000).

Solution: Indexing Table for Sequential Key Mapping

To optimize such queries, an alternative approach can be employed. This involves creating an indexing table that establishes a sequential relationship to the primary key in the target table. By joining this indexing table to the target table and utilizing a WHERE clause, it is possible to retrieve the desired rows more efficiently:

Creating the Indexing Table

CREATE TABLE seq (
   seq_no INT NOT NULL AUTO_INCREMENT,
   id INT NOT NULL,
   PRIMARY KEY (seq_no),
   UNIQUE (id)
);

Populating the Sequence

TRUNCATE seq;
INSERT INTO seq (id) SELECT id FROM mytable ORDER BY id;

Retrieving Rows with Offset

SELECT mytable.* 
FROM mytable 
INNER JOIN seq USING (id)
WHERE seq.seq_no BETWEEN 1000000 AND 1000999;

In this example, 1000 rows are retrieved from an offset of 1,000,000. This method utilizes the indexing table to map the desired offset to the correct rows in the target table, significantly improving query performance compared to traditional offset-based approaches.

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