Why constraints matter in SQL - Quick Recap

Recall & Review

beginner

What is a constraint in a database?

A constraint is a rule applied to a database table to ensure data integrity and correctness. It restricts the type of data that can be inserted or updated.

beginner

Why do constraints matter in databases?

Constraints help keep data accurate, consistent, and reliable by preventing invalid or duplicate data from being stored.

beginner

Name two common types of constraints in SQL.

Two common constraints are PRIMARY KEY, which uniquely identifies each row, and NOT NULL, which ensures a column cannot have null values.

intermediate

How do constraints help when multiple people use the same database?

Constraints prevent users from entering wrong or conflicting data, so everyone sees accurate and consistent information.

beginner

What might happen if a database has no constraints?

Without constraints, the database could have duplicate, missing, or incorrect data, making it unreliable and hard to trust.

What does a PRIMARY KEY constraint do?

A Prevents any data from being inserted

B Ensures each row is unique and not null

C Allows duplicate values in a column

D Automatically deletes rows

A PRIMARY KEY uniquely identifies each row and cannot be null.

Which constraint prevents a column from having empty values?

A FOREIGN KEY

B CHECK

C UNIQUE

D NOT NULL

NOT NULL ensures that a column must have a value and cannot be left empty.

Why are constraints important when many users access the same database?

A They prevent invalid or conflicting data

B They make the database bigger

C They allow users to delete data easily

D They slow down the database

Constraints keep data accurate and consistent even with multiple users.

What could happen if a database has no constraints?

A The database will reject all data

B Data will always be correct

C Data might be incorrect or duplicated

D The database will run faster

Without constraints, invalid or duplicate data can be stored.

Which constraint ensures values in a column are unique but can be null?

A UNIQUE

B PRIMARY KEY

C NOT NULL

D CHECK

UNIQUE constraint allows unique values and can accept nulls.

Explain why constraints are important for maintaining data quality in a database.

Think about what happens if wrong data is allowed.

Describe how constraints help when multiple users work with the same database.

Consider how rules keep data trustworthy for everyone.