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The Difference Between UNION and UNION ALL in SQL

When working with SQL, it's important to understand the distinction between the UNION and UNION ALL operators. The main difference between them lies in how they handle duplicate records.

UNION Operator

The UNION operator is used to combine the result sets of two or more SELECT statements. It eliminates duplicate records from the combined result set, ensuring that each record appears only once.

UNION ALL Operator

On the other hand, the UNION ALL operator also combines the result sets of multiple SELECT statements but includes all records, including duplicates. This can result in a larger combined result set compared to using UNION.

It's important to choose between UNION and UNION ALL based on your specific needs. If you want to include all records, even duplicates, in the final result set, then UNION ALL is the right choice. However, if you want to remove duplicate records and ensure each record is unique, then UNION should be used.

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