What is Cascade in SQL?

In SQL, CASCADE means “automatically apply this action to related records” when a change happens in a parent table.

It’s mainly used with foreign key constraints.

Why CASCADE exists

Databases often have parent–child relationships.

Example:

• Users (parent)
• Orders (child → references Users.UserId)
• CASCADE helps keep data consistent without writing extra queries.

Common CASCADE types

1. ON DELETE CASCADE

When a row in the parent table is deleted, all related rows in the child table are deleted automatically.

CREATE TABLE Orders (
    OrderId INT PRIMARY KEY,
    UserId INT,
    FOREIGN KEY (UserId)
        REFERENCES Users(UserId)
        ON DELETE CASCADE
);

What happens:

• Delete a user
• All their orders are deleted automatically

Good for:

• Logs
• History tables
• Dependent data that should not exist without the parent

2. ON UPDATE CASCADE

When the parent key value changes, the child table is updated automatically.

FOREIGN KEY (UserId)
REFERENCES Users(UserId)
ON UPDATE CASCADE

What happens:

• Users.UserId changes
• Orders.UserId updates automatically

Less common because:

• Primary keys usually don’t change

CASCADE vs other options

Example:

ON DELETE SET NULL

Real-world example

DELETE FROM Users WHERE UserId = 10;

With ON DELETE CASCADE:

• User 10 → deleted
• Orders of User 10 → deleted automatically

Without CASCADE:

• Error: Cannot delete because related records exist

Important cautions

• CASCADE can delete large amounts of data unintentionally
• Always understand relationships before using it
• Avoid CASCADE on critical business data unless required

Simple one-line definition

CASCADE in SQL automatically applies delete or update operations from a parent table to its related child records.