How Do MySQL's ORDER BY and LIMIT Clauses Interact to Retrieve Specific Ordered Results?

MySQL's ORDER BY and LIMIT: A Detailed Look at Their Combined Functionality

MySQL queries frequently employ the ORDER BY and LIMIT clauses to refine result sets. This explanation clarifies how these clauses interact to deliver specific, ordered results.

The database executes these clauses in a defined sequence:

1. WHERE Clause Evaluation: Initially, the WHERE clause (if present) filters the data, retaining only rows matching the specified conditions.
2. ORDER BY Sorting: Following the WHERE clause processing, ORDER BY sorts the remaining rows according to the designated column(s). Ascending order is the default; DESC specifies descending order.
3. LIMIT Restriction: Finally, LIMIT selects a predetermined number of rows from the already sorted result set. Only the top n rows (as determined by ORDER BY) are included in the output.

Illustrative Example:

Consider this query:

SELECT article FROM table1 ORDER BY publish_date LIMIT 20

The database first filters table1 (if a WHERE clause exists). Then, it orders the remaining rows in ascending order by publish_date. Lastly, it limits the output to the initial 20 rows, effectively returning the 20 most recently published articles.

In essence, the query ensures that all records are sorted before the top 20 are selected, guaranteeing the retrieval of the truly most recent articles.

The above is the detailed content of How Do MySQL's ORDER BY and LIMIT Clauses Interact to Retrieve Specific Ordered Results?. For more information, please follow other related articles on the PHP Chinese website!