SQL ALTER TABLE

Add, rename or remove columns.

✍️ 3 exercises + code challenge in this lesson

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ALTER TABLE changes the structure of an existing table:

Add a column: ALTER TABLE Customers ADD Phone VARCHAR(20);
Rename a column: ALTER TABLE Customers RENAME COLUMN Phone TO Mobile;
Remove a column: ALTER TABLE Customers DROP COLUMN Mobile;
Rename the table: ALTER TABLE Customers RENAME TO Clients;
Change a type: ALTER TABLE ... MODIFY COLUMN (MySQL) or ALTER COLUMN (SQL Server, PostgreSQL).

Key Takeaways: SQL ALTER TABLE

Mastering SQL ALTER TABLE helps you write clean and reliable SQL code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

SQL ALTER TABLE Code Example

SQL

ALTER TABLE Customers ADD Phone VARCHAR(20);
UPDATE Customers SET Phone = '0300-1112223' WHERE CustomerID = 1;
ALTER TABLE Customers RENAME COLUMN Phone TO Mobile;

SELECT CustomerID, CustomerName, Mobile FROM Customers LIMIT 3;

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SQL ALTER TABLE Practice Exercises

Check what you learned in “SQL ALTER TABLE”.

/ 3 solved

Fill in the blank

Add a column to a table.

 Customers ADD Phone TEXT;

✓ Correct! Not quite. Try again.

Multiple choice

Which ALTER TABLE action renames a column?

RENAME COLUMN MODIFY NAME CHANGE NAME TO SET NAME

✓ Correct! Not quite. Try again.

Code challenge

Add a column Discount INTEGER to Products, set it to 10 for ProductID 1, then select ProductName, Discount for ProductID 1.

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SQL ALTER TABLE

💡 Key Takeaways: SQL ALTER TABLE

SQL ALTER TABLE Code Example

SQL ALTER TABLE Practice Exercises

Key Takeaways: SQL ALTER TABLE