What does the alter table clause do MCQ? This question is a common query among database administrators and developers who are looking to understand the functionality of the ALTER TABLE clause in SQL. The ALTER TABLE clause is a crucial part of database management, allowing users to modify the structure of a table after it has been created. In this article, we will delve into the various aspects of the ALTER TABLE clause and answer the MCQ question that often arises in the field of database administration.

The ALTER TABLE clause is used to add, modify, or delete columns in a table, as well as to rename tables and columns. It is an essential tool for database administrators and developers to maintain and optimize their database structures. Here are some common scenarios where the ALTER TABLE clause is used:

1. Adding a Column: One of the primary uses of the ALTER TABLE clause is to add a new column to an existing table. This can be done using the following syntax:

“`sql
ALTER TABLE table_name ADD column_name data_type;
“`

2. Modifying a Column: The ALTER TABLE clause can also be used to modify the data type or other properties of an existing column. This can be achieved using the following syntax:

“`sql
ALTER TABLE table_name MODIFY column_name new_data_type;
“`

3. Deleting a Column: If a column is no longer needed, it can be removed using the ALTER TABLE clause. The syntax for deleting a column is as follows:

“`sql
ALTER TABLE table_name DROP COLUMN column_name;
“`

4. Renaming a Table or Column: The ALTER TABLE clause can also be used to rename a table or a column. To rename a table, use the following syntax:

“`sql
ALTER TABLE old_table_name RENAME TO new_table_name;
“`

To rename a column, use the following syntax:

“`sql
ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name;
“`

5. Adding Constraints: Constraints can be added to a table using the ALTER TABLE clause to ensure data integrity. Common constraints include NOT NULL, PRIMARY KEY, UNIQUE, and FOREIGN KEY. The syntax for adding a constraint is as follows:

“`sql
ALTER TABLE table_name ADD CONSTRAINT constraint_name constraint_definition;
“`

Understanding the various uses of the ALTER TABLE clause is crucial for database administrators and developers. Now, let’s address the MCQ question: What does the alter table clause do?

The correct answer to the MCQ question “What does the alter table clause do?” is that it allows you to modify the structure of a table by adding, modifying, or deleting columns, renaming tables and columns, and adding constraints. This versatile clause is an essential part of database management and is widely used in SQL to maintain and optimize database structures.