Data Types in SQL

Last Updated: 14th December, 2023

SQL data types describe the information that can be contained in a table column, such as numbers, characters, dates, and binary. There are four groups of SQL data types: Numeric, character, date/time, and binary. Choosing the right data type for each column is necessary to ensure that information is stored and retrieved correctly. 

Introduction

A company called "TechCo" needed to construct a new database framework to store data on almost their items, clients, and orders. They enlisted a group of database engineers to plan and construct the framework utilizing PostgreSQL, a prevalent open-source database administration framework.

To begin with, the engineers had to choose what information sorts to utilize for each field within the database. They knew that PostgreSQL bolsters numerous distinctive data types, each with its claim one of a kind characteristics and utilize cases.

For illustration, they chosen to utilize the "integer" information sort for the "product ID" field since it was a whole number that would never have a fragmentary portion. They also decided to utilize the "text" information sort for the "product name" field since it might contain any combination of letters, numbers, and images.

For the "customer name" field, they chose the "varchar" data sort since it permitted for variable-length strings, which seem to oblige both shorter and longer names. They also utilized the "date" information sort for the "arrange date" field since it required storing particular dates.

Furthermore, they have chosen to utilize the "boolean" data type for a field that would indicate whether an item was in stock. The "boolean" data type may, as it were, have two possible values, true or false, which was idealized for this utilized case.

As the engineers kept on constructing out the database, they found even more data types that might be utilized, such as "timestamp" for storing correct dates and times, "numeric" for putting away exact decimal values, and "array" for storing collections of related information.

Let's discuss each Data type in detail.

Numeric Data Types

• Numeric data types in SQL are utilized to store a variety of numerical values, including whole numbers, fractions, and floating-point numbers with decimal places. Some of the common examples of numeric data types that are offered in SQL databases are:
  • Integers: int, smallint, tinyint - used to store whole numbers
  • Decimals: decimal, numeric - used to store fractions and precise numerical values
  • Floating point: float, real, double, double precision
• These numeric data types allow SQL databases to represent a wide range of mathematical quantities and support calculations on these quantities.
• They provide flexibility in the precision and scale of the numbers that can be stored, ranging from very small to very large values with varying degrees of precision after the decimal point.
• The appropriate numeric data type can be selected based on the SQL Data Types 2 requirements of the applications and calculations that will be performed on the data. These data types play an important role in enabling SQL databases to support quantitative data analysis and other mathematical operations.

Character and String Data Types

PostgreSQL provides several data types for storing character and string data. These include:

1. "char" and "varchar": These data types are used to store variable-length character strings. The main difference between the two is that "char" fields have a fixed length, while "varchar" fields can vary in length up to a maximum specified length.
2. "text": This data type is similar to "varchar" but has no maximum length limit.
3. "citext": This is a case-insensitive version of the "text" data type. When data is inserted or updated in a "citext" field, PostgreSQL automatically converts it to lowercase, making it easy to perform case-insensitive searches.
4. " char(n)": This data type is used to store fixed-length character strings of a specific length "n". For example, "char(10)" would allow a string of exactly 10 characters to be stored.
5. "name": This data type is used to store short, fixed-length strings. It is typically used for storing things like names, identifiers, or codes.
6. "uuid": This data type is used to store universally unique identifiers (UUIDs). These are 128-bit values that are unique across space and time, making them useful for generating unique IDs for records in a database.
7. "JSON" and "JSONB": These data types are used to store JSON (JavaScript Object Notation) data. JSON stores the JSON data in text format, while JSONB stores it in a binary format for faster searching and sorting.
8. "ENUM": This data type is used to define a list of predefined values for a column. This data type allows you to restrict the possible values that can be stored in a column to a specific set of options.

Date and Time Data Types

In PostgreSQL, there are several data types available for storing dates and times:

1. DATE: This data type is used to store dates without time information. Dates can be specified in the format "YYYY-MM-DD".
2. TIME: This data type is used to store times without date information. Times can be specified in the format "HH:MI: SS".
3. TIMESTAMP: This data type is used to store both date and time information. Timestamps can be specified in the format "YYYY-MM-DD HH:MI: SS".
4. TIMESTAMPTZ: This data type is similar to TIMESTAMP, but it also includes time zone information. This can be useful when working with data from different time zones.
5. INTERVAL: This data type is used to store a duration of time, such as "5 minutes" or "3 days".

When working with date and time data, it's important to be aware of the time zone information associated with each data type. PostgreSQL will use the system's local time zone when storing and retrieving data by default. However, you can specify a different time zone by using the appropriate data type or the AT TIME ZONE function in your queries.

Understanding Data Precision

• Data precision in SQL is the total number of digits in a number, including the digits to the right of the decimal point. In SQL, data precision is determined by the column's data type.
• For example, a column with the INT data type will have a much lower data precision than a column with the DECIMAL data type.
• Precision is important in SQL Data Types 3 because it affects the accuracy of calculations and comparisons. A higher precision allows for more accurate calculations.

Working with Binary Data Types

PostgreSQL supports several binary data types that can be used to store and manipulate binary data. These data types include:

1. bytes: The bytes data type allows you to store binary data as a sequence of bytes. You can insert binary data into a byte column using a hex or escape format string. This data type can be used to store any binary data, including images, audio files, and serialized objects.
2. bit: The bit data type allows you to store binary data as a sequence of bits. This data type can be used to store binary flags, masks, and other types of data that can be represented as a series of bits.
3. varbit: The varbit data type is similar to the bit data type but allows you to store variable-length binary data. This data type can be used to store binary data that is not a fixed length.
4. uuid: The uuid data type allows you to store Universally Unique Identifiers (UUIDs) as binary data. A UUID is a 128-bit value that is typically used as a unique identifier in distributed systems.

Choosing the Best Data Type for Your Data

When choosing the best data type for your data in SQL, it is important to consider the purpose of the data and the type of data being stored. Some common data types include strings, integers, floats, and dates. Strings are best for storing text-based data like names, addresses, and phone numbers. Integers are best for storing numerical data like a person's age or a product's price. Floats are best for storing decimal values like currency. Dates are best for storing dates and times. Other data types, such as binary and bit types, can be used to store binary data. It is important to choose the correct data type for the data being stored in order to ensure data integrity and accuracy.

How to Convert Data Types in SQL

1. The CAST() function can be used to convert one data type to another. This function can convert a value from one data type to another. Syntax:

CAST ( expression AS data_type )

Example:

SELECT CAST(123 AS VARCHAR(10)) AS result;

1. To convert a string into a date or datetime data type, the CONVERT() function can be used. This function takes the expression to be converted and the desired data type as arguments. Syntax:

CONVERT (data_type, expression, style)

Example:

SELECT CONVERT(DATETIME,'20-01-2021',105) AS result;

1. The PARSE() function can be used to convert a string into an integer. This function takes the expression to be converted and the desired data type as arguments. Syntax:

PARSE (string_value AS data_type USING culture)

Example:

SELECT PARSE('10' AS INT USING 'en-US') AS result;

Common SQL Data Type Pitfalls

1. Not using the most appropriate data type: Different databases provide different data types, so selecting the most appropriate data type for the data you're storing is important. For example, if you're storing a date, you should use a date data type instead of a string data type.
2. Not considering the size of data: Some data types have different sizes, so it's important to make sure you use the data type with enough size to hold the data you're expecting. For example, if you're expecting a string of length greater than 255 characters, you should use a larger data type such as text or varchar.
3. Not considering data precision: Some data types need to provide more precision for certain data. For example, if you're trying to store a number with many decimal places, you should use a data type such as decimal or float that provides the necessary precision.
4. Not considering data range: Some data types have a limited range, so it's important to make sure you use a data type that is adequate for the range of data you're expecting. For example, if you're expecting numbers greater than 2,147,483,647, you should use a larger data type such as a bigint.

Conclusion

By carefully choosing the appropriate data types for each field, TechCo's database system was able to efficiently store and retrieve information, making it a valuable asset for the company.

Key takeaways

1. Know the data types of your data when designing a database.
2. Choose the right data type for the right data. For example, use INTEGER for a numeric value, VARCHAR for a string, and DATETIME for a date or time.
3. Understand the usage of NULL in SQL when dealing with missing data.
4. Use BLOB for binary data such as images, videos, and other multimedia files.
5. Use ENUM for a field with a limited set of possible values.
6. CHAR and VARCHAR are used for character strings, but CHAR is typically preferred for fixed-length strings.
7. TEXT is used for large strings, such as long blog posts.
8. Use DECIMAL for monetary values and other numbers where precision is important.

Quiz

1. What data type is used to store numerical values in SQL? 

1. Integer 
2. Boolean 
3. Float 
4. String

Answer: a. Integer

2. What data type is used to store true or false values in SQL?

1. Integer 
2. Boolean 
3. Float 
4. String

Answer: b. Boolean

3. What data type is used to store date and time values in SQL? 

1. Integer 
2. Boolean 
3. Float 
4. DateTime

Answer: d. DateTime

4. What data type is used to store text values in SQL? 

1. Integer 
2. Boolean 
3. Float 
4. String

Answer: d. String