SQL Set Operations Video Lecture | Question Bank for GATE Computer Science Engineering - Computer Science Engineering (CSE)

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1. What are set operations in SQL?
Ans. Set operations in SQL are operations that are used to combine or manipulate the results of two or more SELECT statements. They include UNION, INTERSECT, and EXCEPT, which allow you to merge rows, find common rows, and find rows that are unique to one particular result set, respectively.
2. How does the UNION operator work in SQL?
Ans. The UNION operator in SQL is used to combine the result sets of two or more SELECT statements into a single result set. It eliminates duplicate rows from the combined result set and returns only distinct rows. The columns in the SELECT statements must have the same data types and be in the same order.
3. What is the difference between UNION and UNION ALL in SQL?
Ans. The UNION operator in SQL eliminates duplicate rows from the combined result set, while the UNION ALL operator does not. This means that UNION returns only distinct rows, whereas UNION ALL returns all rows from the combined result sets, including duplicates. Therefore, if you want to include duplicate rows in the result, you should use UNION ALL.
4. How does the INTERSECT operator work in SQL?
Ans. The INTERSECT operator in SQL is used to combine the result sets of two or more SELECT statements and return only the rows that are common to all result sets. It compares the rows in each result set and includes only the rows that have the same values. The columns in the SELECT statements must have the same data types and be in the same order.
5. What is the purpose of the EXCEPT operator in SQL?
Ans. The EXCEPT operator in SQL is used to combine the result sets of two SELECT statements and return only the rows that are unique to the first result set. It compares the rows in the first result set with the rows in the second result set and excludes any rows that are found in both. It is useful for finding the rows that do not exist in the other result set. The columns in the SELECT statements must have the same data types and be in the same order.
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