Column data types (INT, VARCHAR, DATE, DECIMAL) in SQL - Mini Project: Build & Apply

Create a Customer Orders Table with Correct Column Data Types

📖 Scenario: You are working for an online store. You need to create a table to store customer orders. Each order has an ID, customer name, order date, and total amount.

🎯 Goal: Create a SQL table called CustomerOrders with columns using the correct data types: an integer for order ID, a string for customer name, a date for order date, and a decimal for total amount.

📋 What You'll Learn

Create a table named CustomerOrders

Add a column OrderID with data type INT

Add a column CustomerName with data type VARCHAR(100)

Add a column OrderDate with data type DATE

Add a column TotalAmount with data type DECIMAL(10, 2)

💡 Why This Matters

🌍 Real World

Online stores and many business applications use tables like CustomerOrders to keep track of sales and customer information.

💼 Career

Knowing how to define tables with correct data types is essential for database design and management roles.

1

Create the table structure

Write a SQL statement to create a table called CustomerOrders with columns OrderID, CustomerName, OrderDate, and TotalAmount. Do not specify data types yet.

SQL

CREATE TABLE CustomerOrders (
    OrderID,
    CustomerName,
    OrderDate,
    TotalAmount
);
-- Your code here

Hint

Start by writing CREATE TABLE CustomerOrders ( and list the column names separated by commas.

2

Add data types for integer and string columns

Modify the CustomerOrders table creation to set OrderID as INT and CustomerName as VARCHAR(100).

SQL

CREATE TABLE CustomerOrders (
    OrderID INT,
    CustomerName VARCHAR(100),
    OrderDate,
    TotalAmount
);
-- Your code here

Hint

Use INT for OrderID and VARCHAR(100) for CustomerName.

3

Add data types for date and decimal columns

Add the data types DATE for OrderDate and DECIMAL(10, 2) for TotalAmount in the CustomerOrders table.

SQL

CREATE TABLE CustomerOrders (
    OrderID INT,
    CustomerName VARCHAR(100),
    OrderDate DATE,
    TotalAmount DECIMAL(10, 2)
);
-- Your code here

Hint

Use DATE for OrderDate and DECIMAL(10, 2) for TotalAmount.

4

Complete the table creation with all data types

Ensure the CustomerOrders table is created with all columns and their correct data types: OrderID INT, CustomerName VARCHAR(100), OrderDate DATE, and TotalAmount DECIMAL(10, 2).

SQL

CREATE TABLE CustomerOrders (
    OrderID INT,
    CustomerName VARCHAR(100),
    OrderDate DATE,
    TotalAmount DECIMAL(10, 2)
);
-- Your code here

Hint

Double-check that all columns have the correct data types and the syntax is correct.

Practice

1. Which SQL data type is best suited to store a person's full name?

easy

A. DECIMAL

B. INT

C. DATE

D. VARCHAR

Solution

1. Step 1: Understand the data type purpose

   VARCHAR is used to store text or strings, like names.

2. Step 2: Match data type to data

   A person's full name is text, so VARCHAR fits best.

3. Final Answer:

   VARCHAR -> Option D

4. Quick Check:

   Text data = VARCHAR [OK]

Hint: Use VARCHAR for any text data like names or addresses [OK]

Common Mistakes:

• Choosing INT for text
• Using DATE for names
• Using DECIMAL for text

2. Which of the following is the correct way to declare a column for storing a price with two decimal places in SQL?

easy

A. price DATE(10,2)

B. price DECIMAL(10,2)

C. price INT(10,2)

D. price VARCHAR(10,2)

Solution

1. Step 1: Identify the data type for decimal numbers

   DECIMAL is used for numbers with fixed decimal places, like prices.

2. Step 2: Check syntax correctness

   DECIMAL(10,2) means total 10 digits, 2 after decimal point, which is correct.

3. Final Answer:

   price DECIMAL(10,2) -> Option B

4. Quick Check:

   Decimal numbers = DECIMAL(precision, scale) [OK]

Hint: Use DECIMAL(precision, scale) for money or precise decimals [OK]

Common Mistakes:

• Using VARCHAR for numbers
• INT with decimals
• DATE for numeric values

3. Given the table definition:
CREATE TABLE Orders (OrderID INT, OrderDate DATE, CustomerName VARCHAR(50), TotalAmount DECIMAL(8,2));
What will be the result of this insert?
INSERT INTO Orders VALUES (101, '2024-05-10', 'Alice', 123.456);

medium

A. The TotalAmount will store 123.46, rounding to 2 decimals

B. The TotalAmount will store 123.456 exactly

C. The insert will fail due to decimal precision error

D. The TotalAmount will store 123

Solution

1. Step 1: Understand DECIMAL(8,2) behavior

   DECIMAL(8,2) stores numbers with 2 decimal places, rounding if needed.

2. Step 2: Analyze the inserted value 123.456

   Since only 2 decimals allowed, 123.456 rounds to 123.46.

3. Final Answer:

   The TotalAmount will store 123.46, rounding to 2 decimals -> Option A

4. Quick Check:

   DECIMAL rounds to defined decimals [OK]

Hint: DECIMAL rounds extra decimals to defined scale [OK]

Common Mistakes:

• Expecting exact 3 decimals stored
• Thinking insert fails
• Assuming truncation without rounding

4. You have this table creation statement:
CREATE TABLE Employees (ID INT, JoinDate VARCHAR(10));
Why might storing dates as VARCHAR cause problems?

medium

A. Because VARCHAR does not enforce date format, leading to inconsistent data

B. Because INT is better for dates

C. Because VARCHAR cannot store text

D. Because DATE type is slower than VARCHAR

Solution

1. Step 1: Understand VARCHAR vs DATE for dates

   VARCHAR stores text without checking if it is a valid date.

2. Step 2: Identify problems with VARCHAR for dates

   Data can be inconsistent or invalid, causing errors in date operations.

3. Final Answer:

   Because VARCHAR does not enforce date format, leading to inconsistent data -> Option A

4. Quick Check:

   Use DATE type to enforce valid dates [OK]

Hint: Use DATE type to keep dates consistent and valid [OK]

Common Mistakes:

• Thinking INT stores dates
• Believing VARCHAR can't store text
• Assuming DATE is slower

5. You want to create a table to store product details including:
- Product ID as a whole number
- Product name up to 100 characters
- Release date
- Price with up to 7 digits total and 2 decimals

Which is the best SQL column definition for the Price column?

hard

A. Price VARCHAR(7)

B. Price INT

C. Price DECIMAL(7,2)

D. Price DATE

Solution

1. Step 1: Understand the requirements for Price

   Price needs to store numbers with 2 decimal places and up to 7 digits total.

2. Step 2: Match data type to requirements

   DECIMAL(7,2) fits perfectly: 7 digits total, 2 after decimal point.

3. Step 3: Eliminate wrong options

   INT stores whole numbers only, VARCHAR stores text, DATE is for dates.

4. Final Answer:

   Price DECIMAL(7,2) -> Option C

5. Quick Check:

   Use DECIMAL for precise decimal numbers [OK]

Hint: Use DECIMAL(total_digits, decimals) for prices [OK]

Common Mistakes:

• Using INT for prices with decimals
• Using VARCHAR for numbers
• Confusing DATE with price