SQL Union Operator Trivia Quiz

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The SQL UNION is used in set operations. Test your knowledge in the use of the SQL UNION operator, and it's various functions in a data set by taking this quiz. You can also brush up on your knowledge of the difference between UNION, UNION ALL and lots more.

• 1.

The SQL UNION Operator enables you draw information from two or more table with the _____

• A.

Value

• B.

Structure

• C.

Rows

• D.

Lines

B. Structure
Explanation
The SQL UNION Operator enables you to draw information from two or more tables with the same structure. This means that the tables involved in the UNION operation should have the same number of columns and compatible data types for each corresponding column. The UNION operator combines the result sets of the tables, eliminating duplicate rows, and returns a single result set. It is useful when you want to combine data from multiple tables into a single result set for analysis or reporting purposes.

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• 2.

To use the SQL UNION Operator, the tables must all have the same number of _____

• A.

Columns

• B.

Sets

• C.

Orders

• D.

Distinct values

A. Columns
Explanation
The correct answer is "Columns". The SQL UNION Operator is used to combine the result sets of two or more SELECT statements into a single result set. In order to use the UNION operator, the tables involved must have the same number of columns. This ensures that the columns from each table can be properly matched and merged in the resulting combined result set.

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• 3.

To do a SQL UNION operation, the _____ types of the corresponding columns must be compatible.

• A.

Row

• B.

Number

• C.

Option

• D.

Data

D. Data
Explanation
In order to perform a SQL UNION operation, the corresponding columns of the tables being combined must have compatible data types. This means that the data types of the columns should be similar or convertible to each other. If the data types are not compatible, the UNION operation cannot be executed successfully.

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• 4.

What kind of rows does the UNION operation eliminate during operation?

• A.

Duplicate Structures

• B.

Duplicate rows

• C.

Duplicate columns

• D.

Duplicate values

B. Duplicate rows
Explanation
The UNION operation eliminates duplicate rows during its operation. This means that if there are multiple rows in the result set that have the same values in all columns, only one of those rows will be included in the final result set. This is useful when combining the results of two or more queries, as it ensures that each distinct row is only included once in the final result.

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• 5.

If you want to keep the duplicate rows during the UNION operation, what keyword can you use?

• A.

INTERSECT

• B.

ALL

• C.

MINUS

• D.

INTEGER

B. ALL
Explanation
The keyword "ALL" can be used to keep duplicate rows during the UNION operation. When "ALL" is specified, all rows from both tables are included, including duplicates. This means that if there are any duplicate rows in the tables being combined, they will be included in the result set.

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• 6.

Which of the following statements is correct?

• A.

UNION does not remove duplicate rows

• B.

UNION ALL does not remove duplicate rows

• C.

UNION ALL removes duplicate rows

• D.

UNION and UNION ALL do the exact same thing

B. UNION ALL does not remove duplicate rows
Explanation
The correct statement is "UNION ALL does not remove duplicate rows." This means that when using the UNION ALL operator in a SQL query, all rows from both tables will be returned, including any duplicate rows. Unlike the UNION operator, which removes duplicate rows and only returns distinct rows.

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• 7.

Which of the following statements is correct?

• A.

UNION is faster than UNION ALL

• B.

Both UNION and UNION ALL compute at the same time

• C.

UNION ALL is faster than plain UNION

• D.

None of the above

C. UNION ALL is faster than plain UNION
Explanation
UNION combines the results of two or more SELECT statements and removes any duplicate rows. UNION ALL, on the other hand, also combines the results of two or more SELECT statements but does not remove duplicate rows. Since UNION ALL does not have the additional step of removing duplicates, it is generally faster than plain UNION. Therefore, the correct statement is "UNION ALL is faster than plain UNION."

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• 8.

To use the SQL UNION operator, the columns in each select statement must also be in the same _____

• A.

Row

• B.

Order

• C.

Table

• D.

Column

B. Order
Explanation
The SQL UNION operator is used to combine the result sets of two or more SELECT statements into a single result set. In order to use the UNION operator, the columns in each SELECT statement must also be in the same order. This means that the columns in the first SELECT statement must be in the same order as the columns in the second SELECT statement, and so on. If the columns are not in the same order, the UNION operator will not work correctly. Therefore, the correct answer is "Order".

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• 9.

Which of these operators selects only distinct values by default?

• A.

UNION

• B.

UNION ALL

• C.

Both

• D.

None of the above

A. UNION
Explanation
The correct answer is UNION. The UNION operator in SQL selects only distinct values by default. It combines the result sets of two or more SELECT statements and removes any duplicate rows from the final result set. On the other hand, the UNION ALL operator does not remove duplicate rows and includes all rows from the result sets of the SELECT statements. Therefore, when you want to eliminate duplicate values from the result set, you should use the UNION operator.

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• 10.

Which one of these statements is correct?

• A.

In each SELECT statement, the columns must not be in the same order

• B.

The columns must have analogous data types

• C.

Within UNION each SELECT statement doesn't have to have the same columns numbers

• D.

The UNION ALL operator selects distinct values by default

B. The columns must have analogous data types
Explanation
The correct answer is that the columns must have analogous data types. This means that when using the UNION operator to combine the results of multiple SELECT statements, the columns being selected must have the same or compatible data types. This ensures that the data being combined is consistent and can be properly merged together.

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• Current Version
• Mar 21, 2023
Quiz Edited by
ProProfs Editorial Team
• Mar 06, 2019
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