How to Use Alter Table – Add Statement in SQL

If you are a software developer working with large databases, you must have encountered a situation where you need to modify an existing table in your database. One of the most common requirements is to add a new column into the table and update the schema. SQL provides a straightforward solution for this through the ALTER TABLE command. This article will discuss the ALTER TABLE – ADD statement and its usage in SQL.

What is Alter Table – Add Statement in SQL?

ALTER TABLE command is a SQL DDL (Data Definition Language) statement that is used to add, modify, or delete a column, constraint, or index in an existing table. The syntax of ALTER TABLE statement is as follows:

ALTER TABLE table_name
ADD column_name datatype constraints;

The ADD statement adds a new column to the table, and the column_name specifies the name of the new column to be added. The datatype specifies the data type of the new column, and constraints are any constraints that need to be defined for the new column.

How to Use Alter Table – Add Statement in SQL

Adding a new column to an existing table using ALTER TABLE in SQL is a simple two-step process. First, you need to create the statement to add the new column using the ALTER TABLE – ADD command, and secondly, you need to execute the statement to commit the changes to the database. The following example adds a new column named ’email’ of the VARCHAR data type to an existing table named ‘users’.

ALTER TABLE users
ADD email VARCHAR(50);

In the above example, we added a new column named ’email’ to the ‘users’ table with a maximum length of 50 characters.

Add a Column with Constraints

Adding constraints to a column is important to ensure data integrity and enforce rules on the data. The following example demonstrates how to add a new column with a not null constraint to an existing table.

ALTER TABLE users
ADD age INT NOT NULL;

In the above example, we added a new column named ‘age’ to the ‘users’ table of the INT data type with a not null constraint.

Modify an Existing Column

If you need to modify an existing column in your table, you can use the ALTER TABLE command to achieve this. The following example demonstrates how to modify the data type of an existing column.

ALTER TABLE users
ALTER COLUMN age FLOAT;

In the above example, we modified the data type of the ‘age’ column to FLOAT.

Frequently Asked Questions

Conclusion

In this article, we discussed the ALTER TABLE – ADD statement and its usage in SQL. We learned that this statement is a powerful tool for software developers, especially when working with large databases. We also covered some frequently asked questions related to ALTER TABLE – ADD statement. Remember that while adding a column using ALTER TABLE – ADD statement, it’s essential to consider the data type and constraints of the new column. This ensures the integrity of the data and makes your database efficient.

📕 Related articles about MySQL

• How to use Concatenation Operator in SQL
• How to use UPDATE Statement in SQL
• MySQL CREATE FUNCTION Statement: An In-Depth Guide
• The Ultimate Guide to MySQL DELETE Statement
• MySQL Prepared: Everything You Need to Know
• How to use Wildcard operators in SQL