PRIMARY KEY constraint in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a primary key on the 'id' column.

SQL

CREATE TABLE users (id INT [1], name VARCHAR(100));

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AFOREIGN KEY

BNOT NULL

CUNIQUE

DPRIMARY KEY

Attempts:

3 left

💡 Hint

Common Mistakes

Using FOREIGN KEY instead of PRIMARY KEY

Forgetting to specify PRIMARY KEY

Using UNIQUE which allows NULLs

The PRIMARY KEY constraint uniquely identifies each record in the table.

2fill in blank

medium

Complete the code to add a primary key constraint named 'pk_order_id' on 'order_id'.

SQL

ALTER TABLE orders ADD CONSTRAINT [1] PRIMARY KEY (order_id);

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Afk_order_id

Bunique_order_id

Cpk_order_id

Didx_order_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'fk_' prefix which is for foreign keys

Using 'unique_' which is for unique constraints

Using 'idx_' which is for indexes

The constraint name for a primary key often starts with pk_ to indicate its purpose.

3fill in blank

hard

Fix the error in the code to correctly declare a composite primary key on 'id' and 'email'.

SQL

CREATE TABLE contacts (id INT, email VARCHAR(255), [1] pk_contacts PRIMARY KEY (id, email));

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ACONSTRAINT

BINDEX

CFOREIGN KEY

DUNIQUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using INDEX instead of CONSTRAINT

Using FOREIGN KEY which is for references

Using UNIQUE which is not a primary key

Composite primary keys require the CONSTRAINT keyword before naming or defining the key.

4fill in blank

hard

Fill both blanks to create a table 'products' with 'product_id' as primary key and 'name' not null.

SQL

CREATE TABLE products (product_id INT [1], name VARCHAR(100) [2]);

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APRIMARY KEY

BFOREIGN KEY

CNOT NULL

DUNIQUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using FOREIGN KEY instead of PRIMARY KEY

Missing NOT NULL on important columns

The product_id column is the primary key, and name must not be null.

5fill in blank

hard

Fill all three blanks to add a primary key constraint named 'pk_emp' on 'emp_id' in the 'employees' table.

SQL

ALTER TABLE employees ADD [1] pk_emp [2] [3] (emp_id);

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ACONSTRAINT

BPRIMARY

CKEY

DINDEX

Attempts:

3 left

💡 Hint

Common Mistakes

Using INDEX instead of CONSTRAINT

Omitting PRIMARY or KEY keywords

The syntax to add a named primary key constraint is: ADD CONSTRAINT pk_emp PRIMARY KEY (emp_id).