SQL06 Jun 20268 min read

Data Types

A beginner-friendly guide to SQL data types, why they matter, common data type groups, and how to use SQL Server data types when creating table columns.

#SQL#Data Types#SQL Server#Beginner

What are data types?

Data types tell SQL what kind of value a column can store.

A column for a salary should store a number. A column for a name should store text. A column for a date should store a date value.

123Numbers

AaText

▦Dates

◷Time values

✓True / false values

💡A data type defines what kind of data is allowed in a column.

Why data types matter

Data types keep data clean, accurate, and easier to query.

They also help SQL Server store values correctly and work with them efficiently.

No.ReasonWhat it means

▣1Store data correctlyEnsures values are saved in the right format.

✓2Prevent invalid valuesHelps avoid errors and bad data.

↗3Improve query performanceLets SQL work faster and more efficiently.

▤4Use storage efficientlySaves space by using the right amount of storage.

#5Make calculations possibleAllows SQL to perform maths and comparisons.

Example

A salary should be stored as a number, not text.

A date of birth should be stored as a date, not a normal sentence.

💡Using the right data type keeps your data accurate and useful.

Common data type groups

Different SQL data types store different kinds of values.

The exact data type names can vary between database systems, but the main idea stays the same.

Data Type GroupExample Values

Aa Text

Names, emails, departments

123 Number

Age, salary, quantity

1.23 Decimal

Price, tax, percentage

▦ Date / Time

DOB, order date, login time

✓ Boolean / Bit

Active, approved, completed

💡In SQL Server, true / false values are commonly stored using BIT.

Creating columns with data types

When you create a table, each column should be assigned a suitable data type.

This helps SQL Server understand what kind of values each column is expected to store.

CREATE TABLE Employees (
    employee_id INT,
    employee_name VARCHAR(100),
    salary DECIMAL(10, 2),
    hire_date DATE,
    is_active BIT
);

SQL Server data types used

INT stores whole numbers.

VARCHAR stores text.

DECIMAL stores money-like or precise number values.

DATE stores dates.

BIT stores 0 or 1.

💡Choosing the right data type helps each column store the correct kind of value.

Example rows

After creating the table, the values should match the data types chosen for each column.

▦Example Rows

employee_idemployee_namesalaryhire_dateis_active

1Amelia Brown42000.002023-04-101

2James Wilson52000.002022-09-151

3Olivia Taylor46000.002024-01-220

In this example:

1employee_id stores whole numbers.

Aaemployee_name stores text.

1.23salary stores decimal values.

▦hire_date stores date values.

✓is_active stores 1 for true and 0 for false.

Key takeaway

💡

Data types make sure every column stores the right kind of value.Choosing the right data type makes your database cleaner, safer, and easier to query.

Learning SQL in order?

Continue from the SQL Roadmap.

Use the roadmap to follow each SQL topic step by step, from relational database basics to advanced query techniques.

Back to SQL Roadmap

Related lessons

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ALTER TABLE

A beginner-friendly guide to ALTER TABLE in SQL, including how to add, change, and remove columns from an existing table.

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A beginner-friendly guide to the SQL CREATE TABLE statement, including table planning, column names, data types, and a SQL Server-friendly example.

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SQL06 Jun 20268 min read

Data Types

A beginner-friendly guide to SQL data types, why they matter, common data type groups, and how to use SQL Server data types when creating table columns.

#SQL#Data Types#SQL Server#Beginner

What are data types?

Data types tell SQL what kind of value a column can store.

A column for a salary should store a number. A column for a name should store text. A column for a date should store a date value.

123Numbers

AaText

▦Dates

◷Time values

✓True / false values

💡A data type defines what kind of data is allowed in a column.

Why data types matter

Data types keep data clean, accurate, and easier to query.

They also help SQL Server store values correctly and work with them efficiently.

No.ReasonWhat it means

▣1Store data correctlyEnsures values are saved in the right format.

✓2Prevent invalid valuesHelps avoid errors and bad data.

↗3Improve query performanceLets SQL work faster and more efficiently.

▤4Use storage efficientlySaves space by using the right amount of storage.

#5Make calculations possibleAllows SQL to perform maths and comparisons.

Example

A salary should be stored as a number, not text.

A date of birth should be stored as a date, not a normal sentence.

💡Using the right data type keeps your data accurate and useful.

Common data type groups

Different SQL data types store different kinds of values.

The exact data type names can vary between database systems, but the main idea stays the same.

Data Type GroupExample Values

Aa Text

Names, emails, departments

123 Number

Age, salary, quantity

1.23 Decimal

Price, tax, percentage

▦ Date / Time

DOB, order date, login time

✓ Boolean / Bit

Active, approved, completed

💡In SQL Server, true / false values are commonly stored using BIT.

Creating columns with data types

When you create a table, each column should be assigned a suitable data type.

This helps SQL Server understand what kind of values each column is expected to store.

CREATE TABLE Employees (
    employee_id INT,
    employee_name VARCHAR(100),
    salary DECIMAL(10, 2),
    hire_date DATE,
    is_active BIT
);

SQL Server data types used

INT stores whole numbers.

VARCHAR stores text.

DECIMAL stores money-like or precise number values.

DATE stores dates.

BIT stores 0 or 1.

💡Choosing the right data type helps each column store the correct kind of value.

Example rows

After creating the table, the values should match the data types chosen for each column.

▦Example Rows

employee_idemployee_namesalaryhire_dateis_active

1Amelia Brown42000.002023-04-101

2James Wilson52000.002022-09-151

3Olivia Taylor46000.002024-01-220

In this example:

1employee_id stores whole numbers.

Aaemployee_name stores text.

1.23salary stores decimal values.

▦hire_date stores date values.

✓is_active stores 1 for true and 0 for false.

Key takeaway

💡

Data types make sure every column stores the right kind of value.Choosing the right data type makes your database cleaner, safer, and easier to query.

Learning SQL in order?

Continue from the SQL Roadmap.

Use the roadmap to follow each SQL topic step by step, from relational database basics to advanced query techniques.

Back to SQL Roadmap

Related lessons

Continue learning SQL

ALTER TABLE

A beginner-friendly guide to ALTER TABLE in SQL, including how to add, change, and remove columns from an existing table.

Read →

CREATE TABLE

A beginner-friendly guide to the SQL CREATE TABLE statement, including table planning, column names, data types, and a SQL Server-friendly example.

Read →

DELETE

A beginner-friendly guide to the SQL DELETE statement, with SQL Server-friendly examples for removing rows from a table safely.

Read →

Previous lesson

DROP TABLE

Next lesson

SELECT Statement

Browse all lessons