What is the difference between alter and update in SQL?

In SQL (Structured Query Language), both ALTER and UPDATE are essential commands used to manipulate data within a database. However, they serve different purposes and operate on different aspects of the database structure. Understanding the distinction between these two commands is crucial for effective database management.

ALTER: Modifying the Structure of a Table

The ALTER command is used to modify the structure of a table in a database. This includes adding, modifying, or deleting columns, as well as altering the data types or constraints of existing columns. The primary use of ALTER is to change the schema of a table without affecting the data stored within it.

For example, if you want to add a new column to an existing table, you can use the following SQL statement:

“`sql
ALTER TABLE employees
ADD COLUMN email VARCHAR(100);
“`

This statement adds a new column named “email” with a VARCHAR data type and a maximum length of 100 characters to the “employees” table.

UPDATE: Modifying the Data within a Table

On the other hand, the UPDATE command is used to modify the data within a table. It allows you to change the values of one or more columns for specific rows based on certain conditions. The primary purpose of UPDATE is to update existing data in the database.

For instance, if you want to update the email address of an employee with a specific ID, you can use the following SQL statement:

“`sql
UPDATE employees
SET email = ‘newemail@example.com’
WHERE id = 1;
“`

This statement updates the email address of the employee with an ID of 1 to “newemail@example.com”.

Difference in Functionality

The main difference between ALTER and UPDATE lies in their functionality:

– ALTER is used to modify the structure of a table, such as adding or deleting columns, changing data types, or modifying constraints.
– UPDATE is used to modify the data within a table, changing the values of one or more columns for specific rows based on certain conditions.

Summary

In summary, ALTER and UPDATE are two distinct SQL commands with different purposes. ALTER is used to modify the structure of a table, while UPDATE is used to modify the data within a table. Understanding the difference between these commands is essential for effective database management and ensures that you can manipulate your database structure and data as needed.