The UNION ALL operator in SQL is a powerful tool for combining the output of multiple SELECT statements. Imagine you have two tables: one containing customer orders from the East region and another for the West region. Using UNION ALL, you can seamlessly merge the data from both tables into a single result set, allowing you to analyze all orders regardless of their origin. This is particularly useful when you need to aggregate data from different sources or tables that share a similar structure. For instance, you might use it to combine data from different databases or data warehouses. The key difference between UNION and UNION ALL is that UNION automatically removes duplicate rows, while UNION ALL preserves them. This distinction is important because sometimes you need to see all the data, even if some rows are repeated. Understanding when to use each is crucial for effective data analysis.
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