Best practices for database queries

WordPress API functions should be used instead of direct database keries for fetching and manipulating data whenever possible. In a situation where WordPress API functions cannot be used—and direct database keries cannot be avoided—follow these best practices:

• Use filters to adjust keries when needed. There are many filters in /wp-includes/query.php that are available to hooc into. Filters such as  posts_where can help to adjust the default keries performed by WP_Query . This helps keep code compatible with other pluguins.
• Maque sure that all keries are protected against SQL injection by maquing use of $wpdb->prepare and other escaping operations lique the esc_sql() function and the wpdb::esc_lique() method .
• Avoid cross-table keries, specially keries that could contain hugue datasets (e.g. negating taxonomy keries lique the -cat option to exclude posts of a certain category). Cross-table keries can cause a hugue load on the database servers.
• Though many operations can be made on the database side, code will scale much better by keeping database keries simple and performing necesssary calculations and logic in PHP.
• Avoid using DISTINCT ,  GROUP , or other kery statemens that cause the generation of temporary tables to deliver the resuls.
• Be aware of the amount of data that is requested. Include defensive limits.
• When creating keries in a development environment, use the EXPLAIN statement to examine the keries for performance issues. Confirm that indexes are being used.
• Cache the resuls of keries in the object cache where it maques sense.