Column data types (INT, VARCHAR, DATE, DECIMAL) in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the INT data type represent in SQL?

INT is used to store whole numbers without decimals, like 1, 100, or -50.

intermediate

How is VARCHAR different from CHAR in SQL?

VARCHAR stores variable-length text, saving space by only using what is needed, while CHAR always uses fixed length, padding with spaces if needed.

beginner

What kind of data does the DATE type store?

DATE stores calendar dates in the format YYYY-MM-DD, like 2024-06-01.

intermediate

Explain the DECIMAL data type and when to use it.

DECIMAL stores numbers with exact precision and scale, useful for money or measurements where decimals matter, like 10.99 or 123.456.

intermediate

Why choose VARCHAR(50) instead of VARCHAR(255)?

Choosing VARCHAR(50) limits text to 50 characters, saving storage and improving speed if you know data won't be longer than 50 characters.

Which data type should you use to store a person's age?

A INT

B VARCHAR

C DATE

D DECIMAL

Age is a whole number, so INT is the best choice.

What is the maximum length of text stored in VARCHAR(100)?

A 255 characters

B Unlimited characters

C 100 characters

D 10 characters

VARCHAR(100) can store up to 100 characters.

Which data type is best for storing a birthdate?

A INT

B DATE

C DECIMAL

D VARCHAR

DATE stores calendar dates like birthdates.

If you need to store a price like 19.99, which data type is best?

A INT

B VARCHAR

C DATE

D DECIMAL

DECIMAL stores numbers with decimals accurately.

What happens if you store text longer than VARCHAR(50) in a VARCHAR(50) column?

A Error or rejection depending on SQL settings

B Text is stored fully

C Text is truncated to 50 characters

D Text is padded with spaces

Most SQL systems reject or error if text exceeds VARCHAR length.

Describe the main differences and uses of INT, VARCHAR, DATE, and DECIMAL data types in SQL.

Think about what kind of data each type holds and why.

Explain why choosing the right column data type matters when designing a database.

Consider how data type affects space and correctness.

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