SQL Server functions?

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• SQL Server Functions---Union and UNION ALL differences

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If we need to display the results of the two SELECT statements as a whole, we need to use the union or UNION ALL keyword. Union (or union) is the function of merging multiple results together to display them.

the difference between Union and UNION ALL: Union automatically compresses duplicate results in multiple result sets, and union ALL displays all results, whether duplicates or not.

Union: Set operation on two result sets, excluding duplicate rows, and sorting the default rules;

The Union will filter out duplicate records after the table link is made, so the resulting set of results will be sorted after the table is connected, the duplicate records are deleted and the results returned. Most of the actual applications do not produce duplicate records, most commonly, the process table and the History table Union

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SQL Server functions?