1. Which SQL command is used to create a new table in a database?
a) INSERT
b) CREATE TABLE
c) UPDATE
d) ALTER
Answer: b) CREATE TABLE
Explanation: The CREATE TABLE command is used to create a new table in a database. It specifies the table name and its columns along with their data types and constraints.
2. What SQL command is used to remove an existing table from a database?
a) DELETE
b) DROP TABLE
c) TRUNCATE TABLE
d) REMOVE
Answer: b) DROP TABLE
Explanation: The DROP TABLE command is used to remove an existing table along with all its data and structure from a database.
3. In SQL, what command is used to modify an existing table structure?
a) MODIFY TABLE
b) ALTER TABLE
c) UPDATE TABLE
d) CHANGE TABLE
Answer: b) ALTER TABLE
Explanation: The ALTER TABLE command is used to modify the structure of an existing table in the database, such as adding, modifying, or dropping columns.
4. Which SQL constraint is used to uniquely identify each record in a table?
a) PRIMARY KEY
b) UNIQUE
c) FOREIGN KEY
d) INDEX
Answer: a) PRIMARY KEY
Explanation: A PRIMARY KEY constraint is used to uniquely identify each record in a table. It ensures that each row in the table is uniquely identifiable.
5. What SQL constraint is used to enforce referential integrity between two tables?
a) PRIMARY KEY
b) FOREIGN KEY
c) UNIQUE
d) INDEX
Answer: b) FOREIGN KEY
Explanation: A FOREIGN KEY constraint is used to enforce referential integrity between two tables by ensuring that the values in a column match the values in another table’s column.
6. Which SQL command is used to remove all rows from a table without deleting its structure?
a) DELETE
b) TRUNCATE TABLE
c) DROP TABLE
d) REMOVE
Answer: b) TRUNCATE TABLE
Explanation: The TRUNCATE TABLE command is used to remove all rows from a table without deleting the table structure itself. It is faster and uses fewer system resources compared to DELETE.
7. In SQL, what is used to improve the retrieval performance of a database table?
a) Primary Key
b) Foreign Key
c) Index
d) Cursor
Answer: c) Index
Explanation: An index is used to improve the retrieval performance of a database table by providing quick access to rows based on the indexed columns.
8. Which SQL construct is used to retrieve and manipulate data row by row?
a) Primary Key
b) Foreign Key
c) Index
d) Cursor
Answer: d) Cursor
Explanation: A cursor is used in SQL to retrieve and manipulate data row by row, allowing for more granular control over data processing operations.
9. What SQL constraint ensures that all values in a column are unique?
a) PRIMARY KEY
b) FOREIGN KEY
c) UNIQUE
d) INDEX
Answer: c) UNIQUE
Explanation: The UNIQUE constraint ensures that all values in a column or a combination of columns are unique, thus preventing duplicate entries in the table.
10. Which SQL command is used to add an index to a table?
a) CREATE INDEX
b) ADD INDEX
c) INDEX TABLE
d) ALTER INDEX
Answer: a) CREATE INDEX
Explanation: The CREATE INDEX command is used to add an index to a table, which improves the performance of data retrieval operations involving the indexed columns.