· SQL · 6 min read

SQL Server Data Types and Tables

SQL Server Data Types Overview

When creating columns for SQL Server tables, it’s important to know the data types that you can use. Data types determine what type of data can be stored in a column. In SQL Server, data types are grouped into four categories:

  1. Exact numeric data types - these data types store values in which exact precision is required. Examples of exact numeric data types include int, decimal, and numeric.

  2. Approximate numeric data types - these data types store values in which approximate precision is sufficient. Examples of approximate numeric data types include float and real.

  3. Character string data types - these data types are used to store text data. Examples of character string data types include char, nchar, varchar, and nvarchar.

  4. Date and time data types - these data types are used to store date and time values. Examples of date and time data types include datetime, smalldatetime, date, time, and datetime2.

It’s important to choose the correct data type for each column to ensure that the data is stored efficiently and accurately. For example, if you have a column that only needs to store a date, it’s better to use the date data type instead of the more complex datetime data type.

Here’s an example of how to create a table with the correct data types:

CREATE TABLE MyTable
(
    ID int,
    FullName varchar(50),
    DateOfBirth date
)

In this example, we have a table called MyTable with three columns: ID, FullName, and DateOfBirth. The ID column uses the int data type, the FullName column uses the varchar data type with a maximum of 50 characters, and the DateOfBirth column uses the date data type.

By using the correct data types when creating tables, you can ensure that your data is accurate and efficient.

Numeric Data Types in SQL Server

In SQL Server, numeric data types are used to store values that require exact precision. There are several numeric data types that you can use, including int, bigint, smallint, tinyint, decimal, and numeric.

Here’s an overview of each of these data types:

  • int - This data type is used to store whole numbers between -2,147,483,648 and 2,147,483,647. Example: DECLARE @Value int = 12345

  • bigint - This data type is used to store whole numbers that range from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. Example: DECLARE @Value bigint = 1234567890123

  • smallint - This data type is used to store whole numbers between -32,768 and 32,767. Example: DECLARE @Value smallint = 1234

  • tinyint - This data type is used to store whole numbers between 0 and 255. Example: DECLARE @Value tinyint = 200

  • decimal and numeric - These data types are used to store decimal numbers with exact precision. Both data types can store numbers from -10^38 +1 to 10^38 –1 with up to 38 digits of precision. The difference between decimal and numeric is the way they handle rounding. Example: DECLARE @Value decimal(10, 2) = 1234.56

When choosing a numeric data type, it’s important to consider the range of values that will be stored and the level of precision that is required. For example, if you need to store very large whole numbers, bigint would be the best choice. If you only need to store small whole numbers, tinyint would be a more efficient choice.

Here’s an example of how to create a table that uses numeric data types:

CREATE TABLE MyTable
(
    ID int,
    Quantity decimal(10, 2),
    Price decimal(10, 2)
)

In this example, we have a table called MyTable with three columns: ID, Quantity, and Price. The ID column uses the int data type, while the Quantity and Price columns both use the decimal data type with 10 digits of precision and 2 digits after the decimal point.

By using the appropriate numeric data types when creating tables, you can ensure that your data is stored accurately and efficiently.

String and Character Data Types

In SQL Server, string and character data types are used to store text data. There are four main string and character data types that you can use, including char, nchar, varchar, and nvarchar.

Here’s an overview of each of these data types:

  • char - This data type is used to store fixed-length character strings. If you set the length of a char column to 10, for example, then the column will always store 10 characters. Example: DECLARE @Value char(10) = 'Hello'

  • nchar - This data type is used to store fixed-length Unicode character strings. Unicode is a character set that supports characters from many different languages. If you set the length of an nchar column to 10, for example, then the column will always store 10 characters. Example: DECLARE @Value nchar(10) = N'こんにちは'

  • varchar - This data type is used to store variable-length character strings. If you set the length of a varchar column to 10, for example, then the column can store anywhere from 0 to 10 characters. Example: DECLARE @Value varchar(10) = 'Hello'

  • nvarchar - This data type is used to store variable-length Unicode character strings. If you set the length of an nvarchar column to 10, for example, then the column can store anywhere from 0 to 10 characters. Example: DECLARE @Value nvarchar(10) = N'こんにちは'

When choosing a string or character data type, it’s important to consider the length of the data that will be stored. If you know the length of the data in advance and it will always be the same length, char or nchar would be the best choice because they can be stored more efficiently. If the length of the data varies, varchar or nvarchar would be a better choice.

Here’s an example of how to create a table that uses string and character data types:

CREATE TABLE MyTable
(
    ID int,
    Name varchar(50),
    Description nvarchar(500)
)

In this example, we have a table called MyTable with three columns: ID, Name, and Description. The ID column uses the int data type, while the Name column uses the varchar data type with a maximum of 50 characters and the Description column uses the nvarchar data type with a maximum of 500 characters.

By using the appropriate string and character data types when creating tables, you can ensure that your text data is stored accurately and efficiently.

Summary

SQL Server is a powerful tool for managing data, but it can be difficult to know where to start. In this article, we covered the basics of SQL Server data types and tables to help you get started. We discussed the different types of data that you can store in SQL Server, including numeric data types and string data types, and we showed you how to create tables with columns that use these data types. By understanding the basics of SQL Server data types and tables, you can begin to explore the full capabilities of this powerful database management system. Remember to choose the appropriate data type for each column to ensure that your data is stored accurately and efficiently.

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