Regex Replacement in Oracle: A Step-by-Step Guide to Adding Special Characters in a VARCHAR Column

As a developer, have you ever found yourself dealing with strings that contain a mix of characters, including letters and numbers? Perhaps you’ve encountered a specific use case where you need to insert a special character, such as an underscore (_), between a character and a number in a string. In this article, we’ll delve into the world of regular expressions (regex) and explore how to achieve this goal using Oracle’s built-in regex replacement functionality.

Understanding Regex

Before we dive into the solution, let’s take a moment to understand what regex is and how it works. Regular expressions are patterns used to match character combinations in strings. They’re commonly used in programming languages for tasks such as validating input data or extracting specific information from text.

A regex pattern consists of characters and special symbols that combine to form a search pattern. For example, the pattern a*b matches any string that contains the letter “a” followed by zero or more occurrences of the letter “b”.

The Challenge: Adding Special Characters in a VARCHAR Column

In your question, you mentioned that you want to add an underscore (_) between characters and numbers in a VARCHAR column. For instance, if the column value is ABSC124DBV, you’d like it to appear as ABSC_124_DBV.

The Regex Logic: Matching Characters and Numbers

To achieve this, we’ll use regex patterns that match either a character or a number. We’ll employ two types of patterns:

• Character pattern: ([A-Z]) matches any uppercase letter.
• Number pattern: ([0-9]) matches any digit (0 through 9).
• Regex replacement syntax: \1_\2 represents the matched characters, where \1 refers to the first group ([A-Z]) and \2 refers to the second group ([0-9]).

The Regex Replacement Formula

To insert an underscore between a character and a number, we’ll use two regex replacement steps:

Step 1: Replace ([A-Z])([0-9])

In this step, we match any uppercase letter followed by a digit. We replace the matched sequence with the same letter and digit separated by an underscore (\1_\2).

Step 2: Replace [0-9]([A-Z])

In this final step, we match any digit followed by an uppercase letter. Again, we replace the matched sequence with the same digit and letter separated by an underscore (\1_\2).

The Oracle Query

Here’s the complete Oracle query that uses regex replacement to achieve our goal:

SELECT
    val,
    REGEXP_REPLACE(
        REGEXP_REPLACE(val, '([A-Z])([0-9])', '\1_\2'),
        '([0-9])([A-Z])',
        '\1_\2'
    ) AS output
FROM yourTable;

This query takes the input string val, applies the two regex replacement steps, and returns the modified string with underscores inserted between characters and numbers.

Demo

To illustrate this concept, let’s consider an example:

Suppose we have a table named yourTable containing the following row:

We can use the query above to replace _ with _.

SELECT
    REGEXP_REPLACE(
        'ABSC124DBV',
        '([A-Z])([0-9])',
        '\1_\2'
    ),
    REGEXP_REPLACE(
        REGEXP_REPLACE('ABSC124DBV', '([A-Z])([0-9])', '\1_\2'),
        '([0-9])([A-Z])',
        '\1_\2'
    ) AS output
FROM yourTable;

The resulting output would be:

As you can see, the underscores have been inserted between characters and numbers.

Conclusion

In this article, we explored how to use regex replacement in Oracle to add special characters (in this case, an underscore _) to a string. By employing two regex patterns that match either characters or numbers, we were able to insert underscores between these elements. We also provided a concrete example query and demonstrated its usage.

Last modified on 2024-05-12