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ALTER vs. UPDATE: What's the Difference?

Edited by Huma Saeed || By Sara Rehman || Published on February 9, 2024
ALTER is used to change the structure of a database table (like adding a column), while UPDATE modifies the data within the table (like changing a value).

Key Differences

ALTER is a Data Definition Language (DDL) command in SQL used to modify the structure of a database table, such as adding or deleting columns, changing data types, or renaming tables. UPDATE, on the other hand, is a Data Manipulation Language (DML) command used to modify existing data within the rows of a table. It can change the values of specified columns in one or multiple rows.
Sara Rehman
Feb 09, 2024
The ALTER command is crucial when the structure of a database table needs to be altered without affecting the data contained within it. It allows for changes that can impact how data is organized and stored. The UPDATE command, in contrast, is used for modifying the data within the database without altering the table's structure. It's used when the existing data in the database needs to be revised or corrected.
Sara Rehman
Feb 09, 2024
When using ALTER, the changes made to the table structure can have significant implications on the database design and integrity. It's a command that needs careful planning and consideration. UPDATE is used for regular operations within the database, such as changing a customer's address or updating a product price. It's a more frequently used command compared to ALTER as data often requires updates based on business operations.
Huma Saeed
Feb 09, 2024
ALTER can be used to add new constraints to a table, like adding a foreign key or setting a default value for a column. This changes how data will be handled in the future but doesn't modify existing data. UPDATE, however, is used to change existing records within a table, like updating an employee's salary. It directly affects the data currently stored in the database.
Janet White
Feb 09, 2024
The use of ALTER requires understanding the architecture and design of the database, as it can significantly alter how the database functions. It's often used less frequently than UPDATE, as structural changes are not as common as data updates. UPDATE is part of the routine data management operations, ensuring the data within the database remains relevant and accurate.
Aimie Carlson
Feb 09, 2024
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Comparison Chart

Type of Command

Data Definition Language (DDL)
Data Manipulation Language (DML)
Sara Rehman
Feb 09, 2024

Purpose

Modifies the structure of a database table
Modifies the data within the database table
Sara Rehman
Feb 09, 2024

Examples of Use

Adding or deleting columns, changing data types
Changing the values of existing records
Sara Rehman
Feb 09, 2024

Impact

Affects table design and architecture
Affects the content within the existing records
Sara Rehman
Feb 09, 2024

Frequency of Use

Less frequent, structural changes
More frequent, data revision and correction
Sara Rehman
Feb 09, 2024
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ALTER and UPDATE Definitions

ALTER

ALTER affects how data is stored and organized.
ALTER TABLE Products RENAME TO Inventory; changes the name of the Products table to Inventory.
Harlon Moss
Jan 23, 2024

UPDATE

UPDATE ensures data accuracy and relevance.
UPDATE Users SET LastLogin = CURRENT_TIMESTAMP WHERE UserID = 'john_doe'; updates the last login time for a user.
Aimie Carlson
Jan 23, 2024

ALTER

ALTER changes the structure of a database table.
The command ALTER TABLE Students ADD COLUMN Birthdate DATE; adds a new column to the Students table.
Sara Rehman
Jan 23, 2024

UPDATE

UPDATE modifies existing data in a database table.
UPDATE Customers SET Address = '123 New Lane' WHERE CustomerID = 1; changes the address of a specific customer.
Sara Rehman
Jan 23, 2024

ALTER

ALTER adds or removes constraints in a table.
ALTER TABLE Orders ADD CONSTRAINT FK_Customer FOREIGN KEY (CustomerID) REFERENCES Customers(ID); adds a foreign key constraint.
Janet White
Jan 23, 2024

UPDATE

UPDATE is used for revising table records.
UPDATE Employees SET Salary = Salary * 1.05; gives a 5% salary raise to all employees.
Sara Rehman
Jan 23, 2024

ALTER

ALTER modifies table architecture in a database.
ALTER TABLE Orders DROP COLUMN Discount; removes a column from the Orders table.
Sara Rehman
Jan 23, 2024

UPDATE

UPDATE changes values in existing database rows.
UPDATE Products SET Price = Price - 10 WHERE Category = 'Electronics'; reduces the price of all electronics.
Sara Rehman
Jan 23, 2024

ALTER

ALTER is used to redefine a table's schema.
ALTER TABLE Employees ALTER COLUMN Salary DECIMAL(10,2); changes the data type of the Salary column.
Huma Saeed
Jan 23, 2024

UPDATE

UPDATE is part of regular data management.
UPDATE Orders SET Status = 'Shipped' WHERE OrderID = 500; updates the status of an order.
Janet White
Jan 23, 2024

ALTER

To change or make different; modify
Altered my will.
Sara Rehman
Jan 22, 2024

UPDATE

To alter so as to be up to date
Update a textbook.
Update the files.
Sara Rehman
Jan 22, 2024

FAQs

Can ALTER add a new column to a table?

Yes, ALTER can add new columns to an existing table.
Sara Rehman
Feb 09, 2024

What can you not do with an ALTER command?

ALTER cannot modify existing data within the table.
Sara Rehman
Feb 09, 2024

Can ALTER change a column's data type?

Yes, it can change the data type of a column.
Sara Rehman
Feb 09, 2024

Does UPDATE change the table structure?

No, UPDATE only modifies the data within the table, not its structure.
Sara Rehman
Feb 09, 2024

What is the purpose of the UPDATE command?

To change or correct existing data within database table rows.
Huma Saeed
Feb 09, 2024

Is ALTER a DML command?

No, it's a Data Definition Language (DDL) command.
Sara Rehman
Feb 09, 2024

Does ALTER work on multiple tables at once?

No, it typically works on one table at a time.
Janet White
Feb 09, 2024

Can UPDATE affect multiple rows at once?

Yes, UPDATE can modify multiple rows based on the given criteria.
Sara Rehman
Feb 09, 2024

Is UPDATE used for adding new rows?

No, UPDATE is only for modifying existing rows; INSERT is used for adding new rows.
Janet White
Feb 09, 2024

Does UPDATE need a WHERE clause?

While not mandatory, a WHERE clause is recommended to target specific rows.
Janet White
Feb 09, 2024

What happens if you omit the WHERE clause in an UPDATE statement?

It can potentially update all rows in the table, which might be unintended.
Aimie Carlson
Feb 09, 2024

What does ALTER do in SQL?

Modifies the structure or design of a database table.
Sara Rehman
Feb 09, 2024

Does the UPDATE command affect database performance?

Yes, especially if it involves large data sets or lacks proper indexing.
Aimie Carlson
Feb 09, 2024

Is the UPDATE command reversible?

Yes, if used within a transaction that can be rolled back.
Harlon Moss
Feb 09, 2024

Can ALTER command be rolled back?

No, as a DDL command, it's auto-committed and cannot be rolled back.
Sara Rehman
Feb 09, 2024

What's a common use of UPDATE in databases?

Updating user information, product prices, or order statuses.
Aimie Carlson
Feb 09, 2024

Is ALTER reversible in any situation?

Generally, no, once executed, the changes are permanent.
Aimie Carlson
Feb 09, 2024

Are ALTER commands frequent in database management?

Less frequent compared to UPDATE, as structural changes are less common.
Janet White
Feb 09, 2024

Can UPDATE be used with JOIN?

Yes, UPDATE can be used with JOIN to update rows based on other tables.
Sara Rehman
Feb 09, 2024

Can ALTER remove a column?

Yes, it can permanently remove a column from a table.
Harlon Moss
Feb 09, 2024
About Author
Written by
Sara Rehman
Sara Rehman is a seasoned writer and editor with extensive experience at Difference Wiki. Holding a Master's degree in Information Technology, she combines her academic prowess with her passion for writing to deliver insightful and well-researched content.
Edited by
Huma Saeed
Huma is a renowned researcher acclaimed for her innovative work in Difference Wiki. Her dedication has led to key breakthroughs, establishing her prominence in academia. Her contributions continually inspire and guide her field.

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