SQL and Database Management Quiz

What is a subquery?

• A query within another SQL query

• A query that retrieves data from a single table

• A command to delete data

• A type of database schema

Answer explanation

A subquery is defined as a query within another SQL query. It allows for more complex data retrieval by nesting queries, making it a powerful tool in SQL for filtering and processing data.

Which clause can a subquery be placed in?

• SELECT, FROM, WHERE, or HAVING

• WHERE only

• FROM only

• SELECT only

Answer explanation

A subquery can be placed in multiple clauses: SELECT, FROM, WHERE, and HAVING. This flexibility allows for complex queries and filtering based on the results of other queries, making the correct answer 'SELECT, FROM, WHERE, or HAVING'.

What are schema objects?

• Temporary data storage

• Database objects like tables, views, indexes, and sequences

• Only tables in a database

• Only views and indexes

Answer explanation

Schema objects refer to various database objects, including tables, views, indexes, and sequences. The correct choice encompasses all these elements, while the other options are too limited.

Which of the following is NOT a set operator?

• INTERSECT

• UNION

• JOIN

• MINUS

Answer explanation

JOIN is not a set operator; it is used to combine rows from two or more tables based on a related column. In contrast, INTERSECT, UNION, and MINUS are all set operators that deal with the results of queries.

What does the UNION operator do?

• Returns rows from the first query not in the second

• Returns common rows between two queries

• Combines results and removes duplicates

• Combines results without removing duplicates

Answer explanation

The UNION operator combines the results of two queries into a single result set and removes any duplicate rows. This is why the correct answer is 'Combines results and removes duplicates'.

What is the purpose of the MINUS operator?

• To find common rows between two queries

• To return rows from the first query that are not in the second

• To remove duplicates from the results

• To combine results of two queries

Answer explanation

The MINUS operator is used to return rows from the first query that are not present in the second query. This distinguishes it from other operations like finding common rows or combining results.

Which SQL command is used to create a table?

• SELECT TABLE

• ALTER TABLE

• CREATE TABLE

• DROP TABLE

Answer explanation

The correct SQL command to create a table is 'CREATE TABLE'. The other options serve different purposes: 'SELECT' retrieves data, 'ALTER' modifies existing tables, and 'DROP' deletes tables.

What does the INTERSECT operator do?

• Removes duplicates from the results

• Returns common rows between two queries

• Returns rows from the first query not in the second

• Combines results of two queries

Answer explanation

The INTERSECT operator returns common rows between two queries, effectively filtering the results to show only those records that appear in both datasets.

Which of the following is a function used to customize output?

• Set Operators

• Subqueries

• Single-Row Functions

• DDL Statements

Answer explanation

Single-Row Functions are used to customize output by manipulating individual data values, such as formatting dates or strings. Other options like Set Operators and DDL Statements do not serve this purpose.

What is the purpose of DDL statements?

• To control user access

• To create and manage database structures

• To display data from multiple tables

• To manipulate data

Answer explanation

DDL (Data Definition Language) statements are used to create and manage database structures, such as tables and schemas. This distinguishes them from other types of statements that manipulate or display data.