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What is a UNION in SQL?

Q: What is a UNION in SQL?

Short answer: The UNION operator combines the result sets of two or more SELECT queries into a single result set and removes duplicate records. All SELECT queries must have the same number of columns with compatible data types. Example code SELECT Name FROM Employees UNION SELECT Name FROM Customers; Real-world example (ShopNest) ShopNest’s SQL Server database stores customers, products, and orders. Good indexes and clear foreign keys keep checkout queries fast and safe. Say this in the interview Define — one clear sentence (the short answer above). Example — relate it to a project like ShopNest or your real work. Trade-off — when you would not use it.

Short answer: The UNION operator combines the result sets of two or more SELECT queries into a single result set and removes duplicate records. All SELECT queries must have the same number of columns with compatible data types.

Example code

SELECT Name FROM Employees UNION SELECT Name FROM Customers;

Real-world example (ShopNest)

ShopNest’s SQL Server database stores customers, products, and orders. Good indexes and clear foreign keys keep checkout queries fast and safe.

Say this in the interview

Define — one clear sentence (the short answer above).
Example — relate it to a project like ShopNest or your real work.
Trade-off — when you would not use it.

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