Convert Varchar to Int in SQL

In SQL, it is common to store data in different formats like VARCHAR, INT, FLOAT, etc. based on the needs of the application. However, sometimes we may need to convert a VARCHAR column to an INT for performing arithmetic operations, comparisons or other logical queries that require integer values.

This article will explore various ways to convert VARCHAR (string) data types to INT in SQL using the built-in functions the potential pitfalls and examples.

Why Convert VARCHAR to INT?

While working with databases we may need to convert VARCHAR to INT in the following scenarios ?

• Data Processing: Many databases store numeric data as strings for flexibility. But when you need to perform calculations, aggregations, or filtering we must convert the string data to integers.
• Data Validation: Ensuring the correct data type before performing any operation can help prevent errors such as trying to perform the arithmetic operations on the strings.
• Performance: Integer operations are generally faster and more efficient than string operations, especially with large datasets.

The Different SQL databases provide specific functions for data type conversion. Below are methods to convert VARCHAR to INT for major SQL databases like MySQL, SQL Server, and PostgreSQL.

Using CONVERT() Function (SQL Server and MySQL)

The CONVERT() function is used in SQL Server and MySQL to convert one data type to another. It is commonly used when the target data type needs to be explicitly specified.

Syntax

Following is the syntax of the CONVERT() function ?

CONVERT(data_type, expression)

Example in SQL Server

Following SQL query converts a string value to an integer ?

SELECT CONVERT(INT, '45678') AS converted_value;

Example in MySQL

Following is the MySQL query ?

SELECT CONVERT('45678', UNSIGNED) AS converted_value;

Using TO_NUMBER() Function

In Oracle databases, the TO_NUMBER() function is used to convert strings to numbers.

Syntax

Following is the syntax of the TO_NUMBER() function ?

TO_NUMBER(expression)

Example

Following is an example of this function ?

SELECT TO_NUMBER('67890') AS converted_value FROM dual;

This converts the string '67890' to an integer in Oracle.

Using the CAST() Function

The CAST() function is used to convert one data type to another.

Example

Following is an example of the CAST() function

SELECT CAST('54321' AS INT) AS converted_value;

Following is the output of the above query ?

converted_value
------------------
54321

Conclusion

Converting VARCHAR to INT is a common task in SQL especially when dealing with databases where numeric data is stored as text. The SQL provides various methods like CONVERT() and TO_NUMBER() for this conversion across the different database platforms. Proper error handling is crucial especially when working with data that might contain invalid numeric values.