SQL Data Types

When you create a database table, one of the biggest decisions is picking the right data type for each column.

A data type tells the database what kind of info goes in that column. It's like the rules of the game—controls how data gets stored, validated, and processed.

Think about it: a person's name is text. Their age is a number. Storing both the same way makes no sense because they're different things.

SQL data types keep your data accurate, make queries faster, save storage space, and stop garbage from getting into your database.

In this lesson, you'll learn what data types are, why they matter, what types exist, and how to pick the right one for your tables.

Why Are Data Types Important?

A lot of beginners just pick a data type and move on.

But picking the wrong type causes *real* problems later.

Good data types:

Improve Data Accuracy

Stop bad values from sneaking in.

Save Storage Space

Use only what you need.

Increase Performance

Queries run faster with efficient storage.

Simplify Validation

The database checks automatically.

Improve Database Design

Well-designed tables are easier to maintain and scale.

Categories of SQL Data Types

Most SQL databases organize types into buckets:

1. Numeric Data Types
2. Character/String Data Types
3. Date and Time Data Types
4. Boolean Data Types
5. Binary Data Types

Let's go through each.

Numeric Data Types

Numeric types store numbers. You use them for:

• IDs
• Prices
• Quantities
• Salaries
• Scores
• Measurements

INT (Integer)

Stores whole numbers.

Example:

Valid values:

1
100
5000
99999

Invalid values:

10.5
Hello
ABC

Common uses:

• Student IDs
• Employee IDs
• Order Numbers

BIGINT

Stores huge whole numbers (bigger than INT).

Example:

Use it when values get *really* large:

• Population databases
• Financial systems
• Large transaction systems

SMALLINT

Stores smaller integer values.

Example:

Useful when:

• Storage optimization matters
• Values stay in a limited range

Examples:

• Age
• Rating Scores
• Small Counters

DECIMAL

Stores exact numbers with decimals.

Example:

Meaning:

Valid examples:

199.99
5000.50
45.75

Common uses:

• Prices
• Salaries
• Banking systems

FLOAT

Stores approximate decimal values.

Example:

Used for:

• Scientific calculations
• Measurements
• Statistical data

⚠️ FLOAT can introduce rounding errors. For money? Use DECIMAL instead.

Character and String Data Types

String types store text:

• Names
• Addresses
• Emails
• Product descriptions

CHAR

Stores fixed-length text.

Example:

If your value is less than 10 characters, it still reserves 10 spots.

Example:

ABC

still takes up 10 character positions.

Common uses:

• Country codes
• Gender values
• Fixed identifiers

VARCHAR

Stores variable-length text.

Example:

A value uses only the space it needs.

Examples:

Rahul
Priya
Amit Kumar

Most modern apps use VARCHAR everywhere.

Common uses:

• Names
• Emails
• Cities
• Product Names

TEXT

Stores *lots* of text.

Example:

Common uses:

• Blog articles
• Product descriptions
• User comments
• Documentation

Date and Time Data Types

Apps need to store dates and times:

• Birth Dates
• Order Dates
• Login Times
• Event Schedules

SQL has specialized types for this.

DATE

Stores just a date.

Example:

Sample value:

2026-08-15

Common uses:

• Birth dates
• Joining dates
• Event dates

TIME

Stores just time.

Example:

Sample value:

14:30:45

Useful for:

• Shift schedules
• Appointment times
• Timetables

DATETIME

Stores both date and time.

Example:

Sample value:

2026-08-15 14:30:45

Used everywhere in business apps.

TIMESTAMP

Stores date and time, often auto-updating.

Example:

Common uses:

• Record creation time
• Last update tracking
• Activity logs

Boolean Data Types

Boolean values are true or false.

Example:

Possible values:

TRUE
FALSE

Apps use booleans for:

• Active users
• Completed tasks
• Email verification
• Subscription status

Example:

Binary Data Types

Binary types store raw binary data:

• Images
• Audio files
• Documents
• Videos

BLOB

BLOB = Binary Large Object.

Example:

Use it when storing binary content directly in your database. Though honestly, most modern apps store files separately and just save the path.

Data Types in a Real Table

Look at an employee table:

Each column uses a different type based on what it stores.

This creates an efficient, organized database.

Choosing the Correct Data Type

Picking the right data type is fundamental to good database design.

Ask yourself:

Is the value numeric?

Use:

INT
DECIMAL
FLOAT

Is the value text?

Use:

Is the value a date?

Use:

Is the value true or false?

Use:

The goal: pick the best fit without wasting storage.

Common Beginner Mistakes

Using VARCHAR for Everything

Bad:

Good:

Numbers should use numeric types.

Using FLOAT for Money

Bad:

Good:

DECIMAL gives you precision.

Using Large Data Types Unnecessarily

Avoid:

when:

works fine.

Pick the smallest practical type.

Best Practices

Use Appropriate Data Types

Match the type to your actual data.

Avoid Excessive Lengths

Don't use:

for a first name field.

Use DECIMAL for Financial Data

Accuracy matters.

Use DATE Types for Dates

Don't store dates as plain text.

Plan for Future Growth

Think about how data might expand.

Summary

SQL data types define what kind of data goes in a column. They're crucial for database design because they keep your data accurate, make queries faster, save storage, and maintain integrity.

In this lesson, you learned:

• What data types are
• Why data types matter
• Numeric data types
• String data types
• Date and time data types
• Boolean data types
• Binary data types
• Best practices for picking types

Picking the right data type is foundational to professional database design.

Next Step

Continue to the next lesson:

SQL Operators →