How to Limit the Number of Rows Returned by a SQL Query?

Efficiently Retrieving Limited Rowsets in SQL

Working with large datasets often necessitates limiting the number of rows returned by a SQL query to improve performance and manage resource consumption. Different database systems employ distinct syntax for this purpose.

SQL Server: Utilizing the TOP Clause

In SQL Server, the TOP clause, used in conjunction with ORDER BY, restricts the result set to a specified number of rows. The general syntax is:

<code class="language-sql">SELECT TOP n ...
ORDER BY [column_name]</code>

Here, n represents the desired number of rows. For example:

<code class="language-sql">SELECT TOP 10 a.names, COUNT(b.post_title) AS num
FROM wp_celebnames a
JOIN wp_posts b ON INSTR(b.post_title, a.names) > 0
WHERE b.post_date > DATE_SUB(CURDATE(), INTERVAL 1 DAY)
GROUP BY a.names
ORDER BY num DESC</code>

This query returns the top 10 results based on the num column in descending order.

MySQL: Employing the LIMIT Clause

MySQL uses the LIMIT clause to achieve the same outcome. The syntax is:

<code class="language-sql">SELECT ...
ORDER BY [column_name] LIMIT n</code>

Applying this to the example query:

<code class="language-sql">SELECT a.names, COUNT(b.post_title) AS num
FROM wp_celebnames a
JOIN wp_posts b ON INSTR(b.post_title, a.names) > 0
WHERE b.post_date > DATE_SUB(CURDATE(), INTERVAL 1 DAY)
GROUP BY a.names
ORDER BY num DESC
LIMIT 10</code>

This query, like the SQL Server example, returns the top 10 rows ordered by num in descending order. Using these techniques ensures efficient retrieval of data subsets from even the most complex queries.

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