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POS 410 Week 5 DQ 2

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Week #5 DQ 2 - Multiple WHERE statements can accomplish almost everything that a UNION
can. TRUE OR FALSE. Justify your answer. This question is not asking which method is the
best choice. It is simply asking is it possible.
I don't really have any sources backing up this opinion (and it is definitely an opinion), but I
think that a JOIN in combination with a WHERE can do most of the functions of the UNION
clause. The one significant difference between a SELECT with a WHERE or a JOIN and a
SELECT with a UNION is that the SELECT with a JOIN or WHERE adds columns to the query
whereas the SELECT with a UNION adds rows to the query. Since a UNION combines multiple
queries from different tables, that is similar to a JOIN (although the tables used in the UNION
clause do not have to be related as they do in a JOIN) in that you can get results from multiple
tables. Since the WHERE clause does not allow for data from a different table without that table
being named in the FROM or JOIN, the WHERE clause by itself cannot combine results from
multiple tables.
The possibilities are almost unlimited though if you use sub-selects. Then you can specify
different tables, either joined or not, and obtain the same information as using a UNION although
in a different format (since that would add columns, not rows as the UNION does).
So my final answer is that you need additional SELECT clauses such as JOIN or sub-selects in
addition to a WHERE to perform similar functions to a UNION. A WHERE by itself in a
SELECT statement can't perform the same functions as a UNION.

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