SQL Server Data Types

Introduction

SQL data types are fundamental components in database systems that define the nature of the data that can be stored in tables. They play a crucial role in ensuring data integrity, optimizing storage, and facilitating efficient querying and processing. Each data type specifies the format of the data, such as characters, numbers, dates, or binary values.
The benefits of using SQL data types lie in their ability to enforce consistency, enabling databases to validate incoming data and maintain uniformity throughout the tables. This consistency aids in the accuracy and reliability of the information stored. Additionally, data types contribute to storage optimization by allocating appropriate space for different kinds of data, preventing unnecessary resource consumption. Moreover, they support the execution of specialized operations on specific data formats, enhancing query performance and enabling more complex analytical tasks.
Overall, SQL data types provide a structured and standardized framework for organizing and managing diverse types of data within a database system.

Prerequisites

There are no Prerequisites for this article, save for the ability to read and comprehend.

Common Data Types Table

While this data types chart does not include every available SQL Server data type, it highlights the ones you will use most frequently throughout your DBA career. These core data types form the foundation of effective database design and are essential knowledge for any SQL Server professional.

Explaining Data Types

Choosing the correct data type is one of the most important decisions you make when designing a SQL Server database. Data types define what kind of values a column can store, how much storage space is allocated, and how SQL Server processes and retrieves the data. Selecting the proper data type improves query performance, reduces storage consumption, and prevents data integrity issues. In short, thoughtful data type selection leads to faster databases, smaller backups, and fewer surprises as your data grows.
In the sections below, we’ll examine commonly used SQL Server data types, including numeric, character, binary, and date/time types. For each data type, you’ll see its value range, storage size, and recommended use cases. Whether you’re designing tables for the first time or refining an existing schema, this reference will help you make informed decisions that align with SQL Server best practices.
The following sections explore each data type in greater detail, explaining what it represents, when to use it, and the kind of data it is designed to store. Becoming familiar with these data types until they feel natural will significantly improve your ability to design effective database structures. Proper data type selection forms the foundation of efficient table design and is essential for building well-structured, high-performing SQL Server databases.
Let me strongly emphasize, you really need to know data types! Yes, it’s that important.

bigint

The bigint data type is an 8-byte signed integer used to store very large whole numbers. It supports values from −2^63 to 2^63−1, making it ideal for identity columns, counters, or financial calculations where values may exceed the range of a standard int. Use bigint when you expect the stored number to grow beyond two billion. Best practice is to avoid using bigint unnecessarily, as it consumes double the storage of int and slightly increases index size and memory usage. Choose it only when future data growth justifies the larger range.

int

The int data type is a 4-byte signed integer storing values from −2^31 to 2^31−1. It is the most commonly used integer type in SQL Server for primary keys, counters, and general numeric data. Use int when you need fast arithmetic operations and sufficient numeric range for most business applications. Best practice is to default to int for identity columns unless you expect extremely large row counts. It provides a good balance between performance, storage efficiency, and numeric capacity.

smallint

The smallint data type is a 2-byte signed integer storing values from −32,768 to 32,767. It is useful when storing small numeric values such as age, quantity, or short counters. Choose smallint when you are certain the values will not exceed its range. Best practice is to use it only when saving storage space is important and the limited range is acceptable. Overusing smallint can lead to overflow errors if data grows beyond expectations.

tinyint

The tinyint data type is a 1-byte unsigned integer storing values from 0 to 255. It is commonly used for status codes, flags, or small enumerated values. Use tinyint when storing small positive numeric indicators. Best practice is to pair tinyint columns with a lookup table or check constraint to make stored codes meaningful and maintain data integrity.

decimal(p,s)

The decimal(p,s) data type stores fixed-precision numeric values where p is total digits and s is digits after the decimal point. It is commonly used for financial or scientific data where exact precision is required. Unlike floating-point types, decimal does not introduce rounding errors. Best practice is to choose the smallest precision that still meets business requirements to conserve storage. Always specify both precision and scale explicitly to prevent default settings that may not suit your data.

numeric(p,s)

The numeric(p,s) data type is functionally identical to decimal(p,s) in SQL Server. It stores exact-precision numbers and is interchangeable with decimal. Use numeric when maintaining ANSI SQL compatibility or matching external schema definitions. Best practice is the same as for decimal: define precision and scale carefully and use it for currency or high-accuracy numeric values.

varchar(max)

The varchar(max) data type stores variable-length non-Unicode character strings up to 2^31−1 characters. It is useful for large text such as descriptions, logs, or JSON data. Use varchar(max) when the text length is unpredictable or exceeds 8,000 characters. Best practice is to avoid it in columns frequently used in indexes, as very large text fields increase I/O and reduce query performance. For smaller predictable strings, prefer varchar(n) instead.

nvarchar(max)

The nvarchar(max) data type stores variable-length Unicode character data up to 2^31−1 characters. It is essential when supporting multilingual text or special characters. Use it for internationalized applications or when storing user-generated content containing diverse languages. Best practice is to use nvarchar only when Unicode support is required because it consumes twice the storage of varchar.

char(n)

The char(n) data type stores fixed-length non-Unicode strings. SQL Server always allocates exactly n bytes, padding shorter strings with spaces. Use char when storing consistently sized values such as country codes, fixed-format identifiers, or status flags. Best practice is to use char only when the data length is truly constant; otherwise, use varchar to avoid wasted storage.

nvarchar(n)

The nvarchar(n) data type stores fixed-length Unicode strings. Like char, it pads unused space but stores each character using two bytes. Use nvarchar(n) for fixed-length international codes or strings requiring Unicode. Best practice is to confirm that fixed-length storage is justified; otherwise, nvarchar(max) or nvarchar(n) with variable length may be more efficient.

varbinary(max)

The varbinary(max) data type stores variable-length binary data such as images, documents, or encrypted values. It can hold very large binary objects. Use varbinary(max) when storing files inside the database is unavoidable. Best practice is to store large files outside the database (for example, in file storage or cloud blob storage) and keep only file references in SQL Server for better performance and backup efficiency.

binary(n)

The binary(n) data type stores fixed-length binary data. SQL Server always allocates exactly n bytes. Use binary when storing consistent-length hashes, encryption keys, or binary codes. Best practice is to use binary only when fixed length is required; otherwise, varbinary provides better storage efficiency.

datetime2

The datetime2 data type is the modern replacement for datetime. It stores dates from January 1, 0001 through December 31, 9999 with configurable fractional-second precision and uses 8 bytes. Use datetime2 for new development requiring accurate date ranges and time precision. Best practice is to prefer datetime2 over datetime for all new SQL Server designs because it is more accurate, more flexible, and standards-compliant.

datetime

The datetime data type stores date and time values from January 1, 1753 to December 31, 9999. It has fixed precision and uses 8 bytes. It remains common in legacy systems. Best practice is to avoid using datetime in new development and instead use datetime2 for better accuracy and a wider date range.

smalldatetime

The smalldatetime data type stores date and time values from January 1, 1900 to December 31, 2079 using only 4 bytes. It has minute-level precision. Use smalldatetime when storage savings matter and minute precision is acceptable. Best practice is to ensure your application does not require seconds or fractional-second accuracy before selecting this type.

For a full list of SQL data types, visit Microsoft's Books Online.