Which operation does the UNION command in SQL perform?

Which operation does the UNION command in SQL perform?

• A. Combines data from two or more tables
• B. Finds unique records in one table
• C. Indexes a table
• D. Merges two databases

Answer: (A)

The UNION command in SQL is designed to combine the results of two or more SELECT statements into a single result set. When using UNION, it gathers all the unique records from each of the SELECT statements, effectively merging the datasets into one. This means that if similar records exist across the combined datasets, they will be displayed only once in the final output. By default, it removes duplicates, so when you want to ensure that your result set contains only distinct rows from multiple tables or queries, UNION is the appropriate choice. This command is particularly useful when you have a similar structure in the tables (same number of columns, compatible data types) and want to create a comprehensive view from multiple sources. Other operations mentioned do not accurately describe the function of the UNION command. For instance, finding unique records in one table specifically refers more to using the DISTINCT keyword, and indexing involves creating data structures for improving query performance, rather than combining data. Merging two databases is a broader process that may entail complex operations beyond the capabilities of just the UNION command.

The UNION command in SQL is designed to combine the results of two or more SELECT statements into a single result set. When using UNION, it gathers all the unique records from each of the SELECT statements, effectively merging the datasets into one. This means that if similar records exist across the combined datasets, they will be displayed only once in the final output.

By default, it removes duplicates, so when you want to ensure that your result set contains only distinct rows from multiple tables or queries, UNION is the appropriate choice. This command is particularly useful when you have a similar structure in the tables (same number of columns, compatible data types) and want to create a comprehensive view from multiple sources.

Other operations mentioned do not accurately describe the function of the UNION command. For instance, finding unique records in one table specifically refers more to using the DISTINCT keyword, and indexing involves creating data structures for improving query performance, rather than combining data. Merging two databases is a broader process that may entail complex operations beyond the capabilities of just the UNION command.