What is the WordPress `WP_Query` tax_query ‘operator’ parameter and how do ‘IN’, ‘NOT IN’, and ‘AND’ differ in the generated SQL?

Question

WordPress Expert — Hard

What is the WordPress `WP_Query` tax_query ‘operator’ parameter and how do ‘IN’, ‘NOT IN’, and ‘AND’ differ in the generated SQL?

Accepted Answer

The 'operator' parameter in the tax_query of WP_Query in WordPress determines how terms are matched. 'IN' matches posts with ANY specified terms, 'NOT IN' excludes posts with those terms, and 'AND' requires posts to have ALL specified terms simultaneously in the SQL query.