MySQL FETCH Clauses

The `FETCH` clause in MySQL is used to retrieve a specific number of rows returned by a query, particularly in combination with the `OFFSET` clause. It is often utilized for pagination when displaying large datasets in smaller segments.

Usage

In MySQL, the `LIMIT` clause is used to limit the number of rows returned by a query, optionally combined with `OFFSET` for pagination. Unlike some other SQL dialects, MySQL does not use a `FETCH` clause.

SELECT column1, column2, ...
FROM table_name
[ORDER BY column1, column2, ...]
LIMIT { number | ALL } OFFSET start;

In this syntax, `LIMIT number` specifies the number of rows to return after the optional `OFFSET`.

Examples

1. Basic LIMIT Usage

SELECT * 
FROM products
LIMIT 10;

This example retrieves the first 10 rows from the `products` table.

2. LIMIT with OFFSET

SELECT * 
FROM orders
ORDER BY order_date
LIMIT 5 OFFSET 10;

Here, the query retrieves 5 rows starting from the 11th row (offset of 10) in the `orders` table, ordered by `order_date`.

3. Pagination with LIMIT and OFFSET

SELECT first_name, last_name
FROM employees
ORDER BY employee_id
LIMIT 10 OFFSET 20;

This query is useful for pagination, retrieving 10 rows after skipping the first 20 employees, ordered by `employee_id`.

Tips and Best Practices

• Combine with ORDER BY. Always use `ORDER BY` to ensure consistent results when using `LIMIT` and `OFFSET`.
• Use for pagination. Leverage `LIMIT` with `OFFSET` for implementing efficient pagination in applications.
• Test performance impact. Fetching large numbers of rows can impact performance; test different `LIMIT` values to optimize based on application needs.
• Understand SQL dialects. Be aware of differences between MySQL's `LIMIT` clause and similar clauses in other SQL dialects like SQL Server or PostgreSQL to avoid confusion.