SQL Set Operations
SQL set operations are clauses that combine the results of two or more SELECT queries into a single result set, based on set theory principles. They include UNION, INTERSECT, and EXCEPT (or MINUS in some databases), which respectively return all distinct rows, common rows, or rows from the first query not in the second. These operations require the queries to have the same number of columns with compatible data types.
Developers should learn SQL set operations for data analysis and reporting tasks where they need to merge, compare, or filter datasets from multiple tables or queries efficiently. For example, use UNION to combine customer lists from different regions, INTERSECT to find common products in two orders, or EXCEPT to identify new users in a database. They are essential for complex queries in relational databases like PostgreSQL, MySQL, or SQL Server.