Chapter 6: Problem 7

How are the OUTER JOIN operations different from the INNER JOIN operations? How is the OUTER UNION operation different from UNION?

Short Answer

Expert verified

INNER JOIN only returns matched records from the tables, while OUTER JOIN returns all the records from one table and matched records from the other. In case of no match, OUTER JOIN returns NULL for every column of the table without a match. UNION operation combines the result-set of the select statements that have the same number of columns, similar data types, and same order while removing duplicates. OUTER UNION, however, returns all records from the tables including unmatched records and does not remove duplicates.

Step by step solution

Understanding INNER JOIN

The INNER JOIN operation returns only the matched records from two tables. Suppose there are two tables, Table A and Table B, when an INNER JOIN operation is performed on these tables, it will return only the records that have matching values in both tables.

Understanding OUTER JOIN

An OUTER JOIN operation, on the other hand, returns all the records from one table (Table A or Table B) and the matched records from the other table. If there is no match, it will result in NULL values for every column of the table that does not have a matching record.

Differences between INNER and OUTER JOIN

The main difference between INNER JOIN and OUTER JOIN lies in the way they handle the non-matching records: INNER JOIN disregards them while OUTER JOIN includes them.

Understanding UNION operation

The UNION operation is used to combine the result-set of two or more SELECT statements. However, for UNION to work, each SELECT statement within the UNION must have the same number of columns, the columns must also have similar data types, and they must also be in the same order.

Understanding OUTER UNION operation

The OUTER UNION operator concatenates the tuples of the participating relations, even if they do not match. If some tuples have no match or counterpart in the other relation, NULL values are used for the missing columns.

Differences between UNION and OUTER UNION

UNION only returns the matched records from the participating tables, eliminating the duplicate values. OUTER UNION, however, returns all the records, including the unmatched records, from the tables and does not eliminate duplicate values.

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How are the OUTER JOIN operations different from the INNER JOIN operations? How is the OUTER UNION operation different from UNION?

Short Answer

Step by step solution

Understanding INNER JOIN

Understanding OUTER JOIN

Differences between INNER and OUTER JOIN

Understanding UNION operation

Understanding OUTER UNION operation

Differences between UNION and OUTER UNION

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