Why table design matters in SQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from the employees table.

SQL

SELECT [1] FROM employees;

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AALL

B*

Ceverything

Dcolumns

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ALL' instead of '*'

Writing column names when asked for all columns

The asterisk (*) selects all columns from the table.

2fill in blank

medium

Complete the code to create a table named customers with an id column as the primary key.

SQL

CREATE TABLE customers (id [1] PRIMARY KEY);

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AINT

BVARCHAR(10)

CTEXT

DDATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using TEXT or VARCHAR for primary key without reason

Choosing DATE type for an id

The INT type is commonly used for primary keys as unique identifiers.

3fill in blank

hard

Fix the error in the code to add a new column named email of type VARCHAR(255) to the users table.

SQL

ALTER TABLE users [1] COLUMN email VARCHAR(255);

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ACHANGE

BMODIFY

CADD

DUPDATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using MODIFY or CHANGE which are for altering existing columns

Using UPDATE which is for data changes

To add a new column, use the ADD keyword in ALTER TABLE.

4fill in blank

hard

Fill both blanks to create a table named orders with order_id as primary key and order_date as a date column.

SQL

CREATE TABLE orders (order_id [1] PRIMARY KEY, order_date [2]);

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AINT

BVARCHAR(100)

CDATE

DTEXT

Attempts:

3 left

💡 Hint

Common Mistakes

Using VARCHAR for order_date

Using TEXT for order_id

Primary keys are often integers (INT), and dates use the DATE type.

5fill in blank

hard

Fill all three blanks to select customer_name and order_date from orders where order_date is after 2023-01-01.

SQL

SELECT [1], [2] FROM orders WHERE [3] > '2023-01-01';

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Acustomer_name

Border_date

Dcustomer_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using customer_id instead of customer_name

Filtering by wrong column in WHERE

You select customer_name and order_date columns, and filter where order_date is greater than the date given.