SQL - Structured Query Language Data Definition Language (DDL) Questions and Answers

Question 1

Which of the following SQL statements is NOT considered a Data Definition Language (DDL) command?

Accepted Answer

UPDATE

Answer

CREATE

Answer

ALTER

Answer

DROP

Question 2

A database administrator needs to remove all rows from a large table named `LogData` but wants to keep the table structure for future use. Which DDL command is the most efficient for this task?

Accepted Answer

TRUNCATE TABLE LogData;

Answer

DELETE FROM LogData;

Answer

DROP TABLE LogData;

Answer

ALTER TABLE LogData EMPTY;

Question 3

You are tasked with adding a new column named `Email` with a data type of `VARCHAR(255)` to an existing table called `Employees`. Which is the correct DDL syntax to accomplish this?

Accepted Answer

ALTER TABLE Employees ADD Email VARCHAR(255);

Answer

ADD COLUMN Email VARCHAR(255) TO Employees;

Answer

CREATE COLUMN Email VARCHAR(255) IN Employees;

Answer

UPDATE TABLE Employees ADD Email VARCHAR(255);

Question 4

Which DDL statement is used to define a new table, including its columns, data types, and constraints?

Accepted Answer

CREATE TABLE

Answer

INSERT TABLE

Answer

DEFINE TABLE

Answer

NEW TABLE

Question 5

A developer wants to change the name of an existing table from `tbl_Users` to `Users`. Which of the following commands should be used?

Accepted Answer

RENAME TABLE tbl_Users TO Users;

Answer

UPDATE TABLE tbl_Users SET NAME = Users;

Answer

MODIFY TABLE tbl_Users RENAME TO Users;

Answer

CREATE ALIAS Users FOR tbl_Users;

Question 6

What is the primary difference between the `DROP TABLE` and `TRUNCATE TABLE` commands?

Accepted Answer

DROP TABLE removes the entire table structure and its data, while TRUNCATE TABLE only removes the data.

Answer

DROP TABLE can be rolled back, while TRUNCATE TABLE cannot.

Answer

DROP TABLE removes only the data, while TRUNCATE TABLE removes the data and structure.

Answer

TRUNCATE TABLE is a DML command, while DROP TABLE is a DDL command.