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What is a database schema? a) The structure or blueprint of the database, including tables, columns, and relationships b) A copy of the database stored for backup purposes c) A table that contains metadata about the database d) A view that shows the data in a table Answer: a) The structure or blueprint of the […]

What is the purpose of the ROLLBACK command in SQL? a) To undo changes made in a transaction b) To commit changes made in a transaction c) To delete a table from the database d) To create a backup of the database Answer: a) To undo changes made in a transaction Explanation: The ROLLBACK command

What does the COMMIT command do in SQL? a) It saves the changes made in a transaction to the database b) It rolls back all changes made in a transaction c) It deletes the current table d) It locks the database to prevent further changes Answer: a) It saves the changes made in a transaction

What is a transaction in a database system? a) A group of SQL statements that are executed as a single unit b) A log of all changes made to the database c) A backup of the database structure d) A query that modifies multiple tables Answer: a) A group of SQL statements that are executed

What is a non-clustered index in a database? a) An index where the logical order of the index does not match the physical order of the rows b) An index used for primary key columns c) An index used to speed up updates and deletes d) An index that enforces referential integrity Answer: a) An

What is the difference between DROP and TRUNCATE in SQL? a) DROP removes the entire table, TRUNCATE removes all rows b) TRUNCATE removes the table and its data, DROP removes only the rows c) DROP removes indexes, TRUNCATE removes constraints d) DROP removes rows based on a condition, TRUNCATE removes the structure Answer: a) DROP

What is a self-join in SQL? a) A join in which a table is joined with itself b) A join that uses only one column c) A join between two unrelated tables d) A join that combines all columns of two tables Answer: a) A join in which a table is joined with itself Explanation:

What is referential integrity in a database? a) Ensuring that foreign key values match primary key values b) Ensuring that all tables are normalized c) Ensuring that data types match between tables d) Ensuring that queries run efficiently Answer: a) Ensuring that foreign key values match primary key values Explanation: Referential integrity is a database

What is the difference between an INNER JOIN and a LEFT JOIN in SQL? a) INNER JOIN returns only matching rows, LEFT JOIN returns all rows from the left table b) LEFT JOIN returns only matching rows, INNER JOIN returns all rows from the left table c) INNER JOIN is faster than LEFT JOIN d)

What is the difference between DELETE and DROP in SQL? a) DELETE removes rows, DROP removes entire tables b) DELETE is faster than DROP c) DROP cannot be rolled back, DELETE can d) DELETE works on indexes, DROP works on tables Answer: a) DELETE removes rows, DROP removes entire tables Explanation: The DELETE command removes

What is a database backup? a) A copy of the database stored in a separate location for recovery purposes b) A log of all transactions in the database c) A snapshot of the database schema without the data d) A security feature that encrypts the data in the database Answer: a) A copy of the

What is the purpose of a UNIQUE constraint in SQL? a) To ensure that all values in a column are different b) To allow only NULL values in a column c) To prevent any changes to the column after insertion d) To allow duplicate values in a table Answer: a) To ensure that all values

Which SQL function is used to return the current date and time? a) NOW() b) GETDATE() c) CURRENT_TIMESTAMP d) All of the above Answer: d) All of the above Explanation: The functions NOW(), GETDATE(), and CURRENT_TIMESTAMP all return the current date and time in SQL. The exact function used may vary depending on the database

What is a transaction log in a database? a) A record of all transactions that have been performed in the database b) A list of active users in the database c) A backup of the database schema d) A list of database queries executed Answer: a) A record of all transactions that have been performed

What is the main advantage of using an index in a database? a) Faster retrieval of data b) Reduced storage space c) Improved security d) Data redundancy Answer: a) Faster retrieval of data Explanation: The main advantage of using an index in a database is faster retrieval of data. Indexes allow the database to quickly

Which of the following SQL commands is used to create a new table? a) CREATE b) ADD c) INSERT d) SELECT Answer: a) CREATE Explanation: The CREATE command in SQL is used to create a new table, database, or other database objects such as views, indexes, or stored procedures. It is an essential part of

What is a composite key in a relational database? a) A key that consists of two or more columns used to uniquely identify a row b) A key that is not unique c) A key used to link multiple tables together d) A key that is automatically generated by the database Answer: a) A key

Which command is used to change the structure of an existing table in SQL? a) ALTER b) MODIFY c) UPDATE d) INSERT Answer: a) ALTER Explanation: The ALTER command in SQL is used to modify the structure of an existing table. It can be used to add, delete, or modify columns, as well as to

What is the purpose of the SQL HAVING clause? a) To filter groups based on a condition after aggregation b) To filter individual rows before aggregation c) To order the result set in descending order d) To calculate the sum of numeric columns Answer: a) To filter groups based on a condition after aggregation Explanation:

What is a foreign key constraint used for in a relational database? a) To enforce referential integrity between two tables b) To prevent null values in a column c) To ensure unique values in a column d) To improve the performance of SELECT queries Answer: a) To enforce referential integrity between two tables Explanation: A

What is the difference between CHAR and VARCHAR data types in SQL? a) CHAR is of fixed length, while VARCHAR is of variable length b) CHAR can store numbers, while VARCHAR cannot c) CHAR is case-insensitive, while VARCHAR is case-sensitive d) CHAR is faster for numeric values, while VARCHAR is faster for text Answer: a)

What is a clustered index? a) An index where the order of the rows in the table matches the order of the index b) An index that is stored separately from the table c) An index used for non-primary key columns d) An index used for full-text search Answer: a) An index where the order

Which of the following commands is used to remove all rows from a table without deleting the table itself? a) DELETE b) DROP c) TRUNCATE d) ALTER Answer: c) TRUNCATE Explanation: The TRUNCATE command is used to remove all rows from a table without deleting the table itself. Unlike DELETE, which removes rows one at

What is the purpose of the GROUP BY clause in SQL? a) To group rows that have the same values into summary rows b) To sort the result set in ascending order c) To limit the number of rows returned by the query d) To delete duplicate rows from a result set Answer: a) To

What is a stored procedure in a database? a) A set of SQL statements that can be executed as a single unit b) A process for backing up a database c) A trigger that runs on every query execution d) A method of indexing data Answer: a) A set of SQL statements that can be