SQL Server Database Engine Data Types

This document provides a comprehensive overview of the data types supported by the SQL Server Database Engine. Understanding these data types is crucial for efficient database design, data integrity, and performance optimization.

Introduction to Data Types

Data types define the type of data that a column, variable, expression, or parameter can hold. Each data type has a specific set of allowable values, storage size, and behavior. SQL Server offers a rich set of data types to accommodate various data storage and manipulation needs.

Categories of Data Types

SQL Server data types can be broadly categorized as follows:

  • Exact Numerics: Integers and monetary values.
  • Approximate Numerics: Floating-point numbers.
  • Date and Time: For storing date and time values.
  • Character Strings: For storing textual data (Unicode and non-Unicode).
  • Binary Strings: For storing raw binary data.
  • Other Data Types: Including XML, spatial data, JSON, and unique identifiers.

Common Data Types and Their Usage

Integer Data Types

Data Type Description Storage Range
TINYINT Unsigned integer. 1 byte 0 to 255
SMALLINT Signed integer. 2 bytes -32,768 to 32,767
INT Signed integer. 4 bytes -2,147,483,648 to 2,147,483,647
BIGINT Signed integer. 8 bytes -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

Approximate Numeric Data Types

Data Type Description Storage Precision
FLOAT Floating-point number. 4 or 8 bytes Approximately 7 or 15 digits
REAL Floating-point number. 4 bytes Approximately 7 digits

Date and Time Data Types

Data Type Description Storage Range
DATE Stores date only. 3 bytes 0001-01-01 to 9999-12-31
TIME Stores time only. 3 to 5 bytes 00:00:00.0000000 to 23:59:59.9999999
DATETIME Stores date and time. 8 bytes January 1, 1753, through December 31, 9999
DATETIME2 Stores date and time with higher precision. 6 to 8 bytes January 1, 0001, through December 31, 9999

Character String Data Types

Data Type Description Storage
CHAR(n) Fixed-length non-Unicode character data. n bytes
VARCHAR(n) Variable-length non-Unicode character data. n + 2 bytes
NCHAR(n) Fixed-length Unicode character data. 2 * n bytes
NVARCHAR(n) Variable-length Unicode character data. 2 * n + 2 bytes

Choosing the Right Data Type

Selecting the appropriate data type for your columns is a critical design decision. Consider the following:

  • Data Integrity: Use data types that accurately represent the data being stored to prevent invalid entries.
  • Storage Efficiency: Choose the smallest data type that can accommodate the full range of possible values to minimize disk space and memory usage.
  • Performance: Data types can impact query performance. For example, numeric types are generally faster for calculations than string types.
  • Application Requirements: Ensure the data type is compatible with the programming languages and applications that will interact with the database.
Note: Always consider the potential for data overflow or truncation when defining data types. Using the smallest appropriate type can prevent these issues.

Advanced Data Types

SQL Server also supports more specialized data types:

  • UNIQUEIDENTIFIER: Stores a 128-bit globally unique identifier (GUID).
  • XML: Stores XML data.
  • JSON: Stores JSON data (supported from SQL Server 2016 onwards).
  • Spatial types (GEOMETRY and GEOGRAPHY): For storing location-based data.
  • VARBINARY(max): For storing large binary objects (BLOBs).
  • VARCHAR(max) / NVARCHAR(max): For storing large character strings.
Tip: For storing large text or binary data, consider using the (max) variants of VARCHAR, NVARCHAR, and VARBINARY.

Further Reading

For more detailed information and specific syntax examples, please refer to the official Microsoft SQL Server documentation: