SQL UNION and UNION ALL operators are essential for combining results from multiple SELECT statements in relational databases. The UNION operator merges rows from different queries, eliminating duplicate rows in the final set. To utilize UNION, the SELECT statements must have the same number of columns, with similar data types and in the same order. Conversely, UNION ALL combines results from SELECT statements without removing duplicates, making it potentially more efficient for scenarios where duplicates are acceptable or desired.
The SQL UNION operator combines results from multiple SELECT statements into a single result set, automatically removing duplicate rows. Each SELECT statement must have the same number of columns, and those columns must have similar data types and be in the same order across the queries.
The UNION ALL operator, in contrast, combines results from multiple SELECT statements but retains all duplicate rows. This operator can be more efficient than UNION because it doesn't require the additional processing time of removing duplicates.
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