What does INTERSECT do?

What does INTERSECT do?

• A. It lists rows that appear in both query results.
• B. It lists rows that appear only in the first query.
• C. It lists all rows from the first query.
• D. It lists rows that appear in either query.

Answer: (A)

INTERSECT finds the common rows between two query results. It returns only those rows that appear in both inputs, matching on every column in the select list. By default, duplicates are removed, so you get distinct rows that exist in both results. The two queries must return the same number of columns with compatible data types. This is useful when you want to know which records are shared by two datasets, such as customers who are both in a loyalty program and have placed an order in a given period. If you need to keep duplicates, some databases offer INTERSECT ALL, but the standard behavior is distinct rows. This differs from listing rows only in the first query (EXCEPT/DIF) or listing all rows from the first query (a simple projection of the first input) or listing rows from either query (UNION).

INTERSECT finds the common rows between two query results. It returns only those rows that appear in both inputs, matching on every column in the select list. By default, duplicates are removed, so you get distinct rows that exist in both results. The two queries must return the same number of columns with compatible data types. This is useful when you want to know which records are shared by two datasets, such as customers who are both in a loyalty program and have placed an order in a given period. If you need to keep duplicates, some databases offer INTERSECT ALL, but the standard behavior is distinct rows. This differs from listing rows only in the first query (EXCEPT/DIF) or listing all rows from the first query (a simple projection of the first input) or listing rows from either query (UNION).