Key SQL Server Data Types and Examples

Microsoft SQL Server, an RDBMS popular for its robust database management capabilities, offers a diverse range of data types to cater to varied data storage needs. However, data practitioners experience a variety of challenges related to the SQL Server data types. From data storage optimization and data integrity to query performance and more, the challenges span several key areas.

Understanding the key SQL Server data types will allow you to effectively use these for efficient data storage and manipulation. Additionally, this knowledge will help write efficient queries for making the most of SQL Server’s powerful database management capabilities. Let’s understand the challenges faced by data practitioners and the different data types in SQL Server with relevant examples.

Challenges Faced by Data Practitioners About Data Types in SQL Server

When you create a table or add a column to a table in SQL Server, you must specify the data type for each column. By specifying this, you can ensure that only the appropriate data type is stored in the column, enhancing data integrity and optimizing performance. A table with inappropriate data types may lead to several issues, such as improper query optimization, data reduction, or performance issues.

Data practitioners are often faced with certain challenges related to SQL Server data types. Here are the challenges that may impact different aspects of database management. 

1. Data Storage Optimization

Different data types require different amounts of storage space. Selecting the right data type is essential to optimize storage. While over-sized data types may consume unnecessary disk space, under-sized ones may result in data truncation. By optimizing the data types, you can reduce storage costs and improve retrieval speed.

Select the data type that matches the kind of data you have. Also, ensure the memory space of the selected data type is minimal yet sufficient for your data needs. This will save storage and improve performance.

2. Data Integrity and Validation

Ensuring that data, especially from external data sources, adheres to defined formats and ranges can be challenging. Choosing the right data types for variables, your tables, and stored procedures will improve performance and data integrity by ensuring correct data is stored within a database.

It’s essential to use proper data types to validate data, like using DATE instead of character or numeric data type for dates.

3. Query Performance

Data types impact how SQL Server stores, processes, and retrieves data. Incorrect data types can lead to inefficient queries, resulting in slow performance.

Consider optimizing data types for your usage. Also, use indexing effectively, considering data types when designing indexes. Using the correct data types will ensure that only appropriate data is stored in each column and significantly enhance query performance.

4. Data Type Conversion and Compatibility

Some implicit and explicit data type conversions are not supported when you convert the data type of one SQL Server object to another. This may lead to errors or unexpected behavior, especially when moving between different SQL Server versions or systems.

5. Memory Utilization and Resource Allocation

Typically, each data type has its own upper and lower limits and memory requirements. Certain data types, such as large object data types, consume significant memory and resources. This affects the overall performance.

By assigning an appropriate data type to a variable or column, you can efficiently use memory. Only the required amount of system memory will be allocated for the data in the relevant column.

You may use SQL Server’s data compression features to reduce the memory utilized. Consider optimizing the use of memory-intensive data types.

6. Indexing and Searching

Poorly written queries can result in high memory usage by consuming excessive memory. To optimize queries, you can use indexes; this will speed up queries and reduce the amount of memory required to execute them.

However, creating efficient indexes can be challenging, particularly when dealing with large text fields or complex data types. A solution to this is to use full-text indexing for large text fields. Also, optimize data types for search operations and avoid table scans by using WHERE clauses to filter results.

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Different SQL Server Data Types

Data Types

SQL Server supports a broad category of SQL standard data types. Based on the storage characteristics, some data types are designated as belonging to the following groups:

• Large Value Data Types: varchar(max), nvarchar(max)
• Large Object Data Types: text, ntext, varbinary(max), xml, image

Let’s look into the details of the different data types in SQL Server.

1. Exact Numerics

This data type stores exact numbers such as integers, decimals, and monetary amounts. The exact numerics are defined by precision and scale.

• int, bigint, smallint, and tinyint data types store integer data of varying ranges. These data types are ideal for storing whole numbers where precision is crucial. Apart from storing exact values, the data types are suitable for performing precise and safe calculations, fastest integer calculations, and avoiding binary-to-decimal rounding errors.

Consider using int for general purposes, smallint or tinyint for smaller ranges (like quantity or age), and bigint for very large values (like population counts).

• decimal and numeric data types store numbers with fixed precision and scale. Both these data types are similar. The storage is based on the number of digits in the number and can range from 5 to 17 bytes.

Financial data such as account balances must be stored as numeric or decimal data types. They’re often used in financial calculations where rounding errors are unacceptable (like interest rates, currency, etc.).

• money and smallmoney data type store currency values.

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Here’s an example of a SQL query involving exact numeric data types:

CREATE TABLE dbo.MyTable  

(  

  MyDecimalColumn DECIMAL(5,2)  

,MyNumericColumn NUMERIC(10,5)  

); 

GO  

INSERT INTO dbo.MyTable VALUES (123, 12345.12);  

GO  

SELECT MyDecimalColumn, MyNumericColumn  

FROM dbo.MyTable;

The output of this will be:

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2. Approximate Numerics

The approximate numeric data types are used to store floating point numbers. These data types are “approximate” because they store an approximation of the value rather than an exact value, which could result in precision errors.

While real stores single-precision floating point numbers using 4 bytes, float stores double precision using 4 or 8 bytes, depending on the precision.

Approximate numeric data types are typically used in scientific calculations where a high degree of precision isn’t critical. Float is suitable for scientific and engineering calculations where precision is less important than range (like astronomical distances). On the other hand, real is suitable for less precise computations.

The two approximate numeric data types in SQL Server are float and real.

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The syntax for the SQL Server float data type is

FLOAT [(n)]

where n is the number of bits used to store the mantissa of the number in scientific notation. It dictates the precision and storage size. While the default n value is 53, if you’re specifying the value of n, it must be between 1 and 53.

SQL Server treats n as one of two possible values. For 1<=n<=24, n is treated as 24, and for 25<=n<=53, it is treated as 53.

Here’s an example query:

DECLARE @Datatype_Float FLOAT(24) = 22.4321

PRINT @Datatype_Float

The output of this query will be 22.4321.

3. Date and Time

SQL Server provides multiple data types specifically to store date and time information. Such data types allow you to store dates, times, or both. There are six different data types in this category.

• date is suitable for scenarios where only the date is important, such as birth dates or event dates.

• Similarly, time is suitable when the time component is of significance, like time logs.

• smalldatetime is often used for applications that don’t require high-time precision, such as weather forecasting applications.

• datetime is commonly used to store date and time information that needs to be accurate to the minute. It can be used to record a timestamp of when an event occurred or when an event was created or modified.

• datetime2 is typically used in scenarios requiring high-precision time, such as financial trading systems, scientific experiment records, etc.

• datetimeoffset is a date and time with time zone awareness. If you’re dealing with time zones that utilize daylight savings time, this is a useful data type.

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Here’s an example code to convert a date value to a datetime value:

DECLARE @date DATE = ’12-10-25′;

DECLARE @datetime DATETIME = @date;

SELECT @date AS ‘@date’,

    @datetime AS ‘@datetime’;

The result will be as follows:

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4. Character Strings

Character Strings data types allow you to define only the character data type, which can be fixed-length (char) or variable-length (varchar) data. These types come in two main categories: Unicode and non-Unicode.

• char(n) can be used to store fixed-length string data.

• varchar(n) is used for storing variable-length string data, such as addresses, emails, text, descriptions, and comments.

• text is suitable for storing large amounts of text data, such as long articles or logs. It can also store binary data, such as image or audio files.

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Here’s an example of a SQL query to show the default value of n when used in a variable declaration:

DECLARE @myVariable AS VARCHAR = ‘abc’;

DECLARE @myNextVariable AS CHAR = ‘abc’;

–The following returns 1

SELECT DATALENGTH(@myVariable), DATALENGTH(@myNextVariable);

GO

The char and varchar data types when used in variable declaration, will return a value of n=1.

5. Unicode Character Strings

Unicode character string data types store either fixed-length (nchar) or variable-length (nvarchar) Unicode character data. This category stores the full range of Unicode characters, which uses the UTF-16 character encoding.

Unicode types require twice as much storage space per character compared to non-Unicode types.

• nchar can be used for fixed-length Unicode data such as foreign language characters.

• nvarchar is suitable for variable-length Unicode text.

• ntext is a legacy type for large blocks of Unicode text and should be replaced by nvarchar(max).

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NOTE: SQL Server provides a hybrid model for storing and processing both relational and JSON data. While there is no dedicated SQL Server JSON data type, JSON text is stored in varchar or nvarchar columns and is indexed as plain text.

6. Binary Strings

Binary string data types are used to store binary data, such as image, audio, and video files of fixed or variable length, in a database location.

• binary data type is typically used to store binary data such as images, audio, and video files. It can also be used to store fixed-length data such as encrypted data or checksums.

• varbinary is also commonly used to store binary files such as images, audio, video, etc. It can also be used to store encrypted data and hash values.

• image data type is typically used for storing binary files like images, sound, and videos. It can store binary data of any size, making it ideal for storing large files.

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Consider the following SQL query:

SELECT CAST( 123456 AS BINARY(4) );

This statement shows the integer value 123456 stored as a binary 0x0001e240.

7. Other Data Types

Apart from the data types mentioned above, SQL Server also supports various other data types. 

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Most of these data types are for specialized use cases. They require a good understanding of the specific requirements and the data type’s behavior. When using these data types, consider how they will interact with other systems; some types may not be supported or might need special handling when moving data to or from different environments.

NOTE: The rowversion data type is also the SQL Server timestamp data type. Rowversion has been available since SQL Server 2005, while TIMESTAMP is deprecated.

Conclusion

Understanding the vast array of SQL Server data formats can provide multiple benefits, including overcoming the common challenges faced by data practitioners. By carefully selecting the appropriate data types, you can optimize storage, maintain data integrity, enhance query performance, and ensure efficient memory utilization.

Each data type in SQL Server serves a unique purpose and caters to specific needs of data representation or storage.  It’s essential to choose the right data type for your specific application. This will help ensure you utilize SQL Server’s capabilities to the best possible extent.

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