Adventures in Machine Learning

Mastering Text Data Types in SQL: Best Practices and Subtypes

The world of data and databases can be quite complicated, which is why it is essential to have a sound understanding of the fundamental concepts, including text data types, in SQL. In this article, we will explore the various character data types and their importance in database management.

Storing Textual Information in SQL

In SQL, there are several data types available for storing textual information. One of the most common types is the character data type.

This data type is used to store alphanumeric characters, also known as strings. A string can contain any combination of letters, numbers, and punctuation marks.

Fixed-Length Character Data Type

The CHAR data type is a fixed-length character type that can store fixed-length strings of up to 8,000 characters. The column length specified in the data model represents the maximum number of characters that can be stored in the particular column.

If the data stored is less than the specified length, extra spaces will be added through a technique known as padding. This can ultimately lead to increased database size, so it is important to monitor the data and account for any potential wasted space.

Variable-Length Character Data Type

In contrast to the fixed-length character data type, the VARCHAR data type is a variable-length character type that can accommodate varying lengths of strings, depending on the data being stored. It is an essential data type as it can drastically save on database size and should be used when the maximum length of the string is not known beforehand.

However, it is crucial to consider the maximum string length when defining a VARCHAR column in any data model. Data profiling of the text data can help define the maximum length for each column.

The maximum length can be calculated by taking the average length of all strings and multiplying by a certain factor for growth. Defining an appropriate column length can save significant space in databases, resulting in faster query processing times.

Very Large Character Data Type

When character data types reach a length greater than 8000 characters, it is necessary to use the CLOB or TEXT data type. These data types are designed to store larger character strings of up to 2 gigabytes.

They are used very carefully, mainly for data normalization.

Characteristics of Text Data Types in SQL

SQL has several data types that can be used to store various types of information, but the most commonly used data types for text are numeric, character, and date. In SQL, text is also case-sensitive.

This means that the usage of uppercase and lowercase letters in a string determines a unique value. As a result, operators like “=” and “<>” used to compare these values can produce incorrect output if the writer does not pay attention to the letter case being used.

To minimize errors in code, text in SQL requires single quotes. When utilizing single quotes incorrectly, a SQL query will likely fail, raising an error.

For example, SELECT name FROM customer WHERE name = Bob; retrieves all customer names that match the string Bob. SQL provides several functions useful for working with text data.

One of these functions is the LENGTH function which returns the length of the string passed as a parameter. Knowing the length of a text field can be useful when creating queries, as it helps the programmer to understand how many characters they are working with and how to manipulate the data effectively.

Comparing Text in SQL

Comparing text data types in SQL can be a bit tricky due to the case-sensitive nature of text. A comparison of strings of different cases can cause unwanted results.

In this scenario, the string comparison function within SQL can assist in determining similar data among strings for exact or partial similarities for the data types being compared.


To efficiently manage databases in SQL, it is essential to know and understand the various data types, especially the text data types. The fixed-length character data type, variable-length character data type, and very large character data type are the most common data types for text in SQL.

Understanding the different characteristics of text data types in SQL, such as the requirement for single quotes and the case-sensitive nature of text, is also crucial. Finally, knowing how to compare text correctly is essential.

By carefully considering text data types in SQL, database management becomes much simpler and streamlined. Storing text data with precision and efficiency is a crucial aspect of SQL database management.

Differentiating between subtypes of character data types in SQL and utilizing best practices can give us better control over our data while keeping the database performant.

Subtypes of Character Data Types in SQL

CHAR Data Type

The CHAR data type is a fixed-length character data type that can store alphanumeric characters, taking up a predetermined number of bytes. Because it is fixed-length, the column size must be declared when creating tables, a primary disadvantage of using CHAR data type when it comes to storage efficiency.

However, CHAR data consumes less CPU resources due to the constant byte allocation.

NCHAR Data Type

The NCHAR data type is a fixed-length character data type that stores Unicode-encoded data. Each NCHAR occupies two bytes, allowing it to store text data from all over the world.

When data is foreign-language centric, the NCHAR data type is more effective than the CHAR data type because it can’t store anything outside the fixed byte allocation.


The VARCHAR data type produces columns that have a variable length, specifying the maximum number of characters that can store. However, this data type is suited only for strings up to 8000 characters.

When defining VARCHAR data type columns, it is best to perform data profiling to determine the maximum length of a string when performing data profiling. The VARCHAR data type chunk sized data along with the read or write deadlocking of the database server.

VARCHAR2 Data Type

VARCHAR2 data type is another implementation of the variable-length string data type that supports string sizes greater than 8000 characters. VARCHAR2 supports bulk-reading of chunks of data, fault tolerance, and is more powerful.

It serves as a superior alternative to the VARCHAR data type for data sets of large size. N


Same as NCHAR to CHAR, a Unicode version of VARCHAR is NVARCHAR, with the “N” indicating “national language.” Hence, the NVARCHAR data type is more suitable for multinational companies and their databases.

CLOB Data Type

The CLOB data type is designed to store large volumes of text data that are too big for the VARCHAR data type and its sub-types. Data in CLOB columns can be UTF-16 or UTF-32, and therefore it is suitable for multilingual text data.

CLOB data types should be used carefully since they often lead to slower database synthesis.

TEXT Data Type

The TEXT data type is often used for storing large amounts of free-form text data, such as comments on records. This data type is widely used in many SQL databases, including MySQL, PostgreSQL, etc.

It provides developers with enough space to accommodate large textual data. Best Practices for

Storing Textual Information in SQL

Plan ahead for Column Length

Before defining the columns for text data types, it is best to perform data profiling to determine the maximum length of the strings involved in the data set.

Defining the length of the columns must be done before creating our data models and defining tables. This ensures that enough space is allocated for data entry while avoiding excess memory usage and storage inefficiencies.

Avoid Padding with Fixed-Length Data Types

With fixed-length data types like CHAR, there may be a need to pad extra spaces when input data is of a smaller size than the defined column length. Extra space allocation results in a large database footprint, increasing costs and affecting performance.

Instead, it is best to normalize data to avoid the padding of extra characters.

Profile Data for Variable-Length Data Types

While using VARCHAR and its subtypes, it is best to perform data profiling to determine the maximum length of the strings involved in the dataset. Defining the maximum length of the column before creating tables ensures adequate data space allocation, leading to better performance with space utilization.

The potential problem for failing data profiles is to increase column sizes to account for future growth but bear in mind that this can waste database memory space and negatively impact performance. Use

Very Large Character Data Type with Caution

It is best to use Very Large Character data types like CLOB cautiously, as they lead to slower database synthesis, disk, and CPU load, and should, in most cases, be used in a normalized fashion with other data types^2.

Moreover, the normalization process ensures that the database avoids the redundancy of data, leading to greater performance and efficiency.

Ultimately, there are many performance considerations when it comes to managing data in SQL databases.

It is always best to consider the size of the data while creating table designs and determine appropriate data type usage to avoid redundancy and improve performance.


Subtypes of character data types in SQL and best practices when dealing with text data are imperative to excellent SQL performance and database management. By monitoring the length of different text strings and performing data profiling, developers can ensure that data models are optimized for performance, and memory usage is efficient.

Choosing the right data type ensures proper resource utilization and that SQL servers remain streamlined and cost-effective. In conclusion, this article has delved into the importance of understanding the various subtypes of character data types in SQL and following best practices when storing textual information in databases.

By differentiating between fixed-length character data types like CHAR and NCHAR, variable-length character data types like VARCHAR and NVARCHAR, and very large character data types like CLOB and TEXT, database managers can ensure optimal performance for their SQL servers. Best practices, such as planning ahead for column length, avoiding padding with fixed-length data types, performing data profiling for variable-length data types, and using very large character data types with caution, are essential considerations to keep in mind when managing data in SQL.

By following these guidelines, developers can reduce redundancy, allocate database memory efficiently, and improve performance, ultimately leading to cost-effective and streamlined SQL databases.

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