Published on

September 24, 2007

Exploring Regular Expressions in SQL Server

Regular expressions are a powerful tool for text processing and pattern matching. In SQL Server, regular expressions can be used to transform, search, and find patterns in text data. In this article, we will explore the regular expression tools available in SQL Server and how they can be used in your database and application development.

Installation

Before we dive into the regular expression tools, let’s quickly go over the installation process. The SQL 2000 DBA Toolkit, which includes the regular expression tools, can be easily installed by copying the DLL files to the MSSQL\BINN directory and running the INSTALL.SQL script. Detailed installation instructions can be found in the README.RTF file included in the toolkit’s \DOCS directory.

fn_regex_match

The first regular expression tool we’ll discuss is the fn_regex_match function. This function allows you to check if a search string matches a specified regular expression. It accepts three parameters: the search expression (in Perl syntax), the search string, and optional user-defined options. The function returns ‘Y’ if a match is found, and ‘N’ otherwise.

Here’s an example usage of fn_regex_match:

SELECT dbo.fn_regex_match ('\d+', '$1,234.56', NULL)

In this example, the regular expression ‘\d+’ matches one or more numbers, and the search string ‘$1,234.56’ contains a pattern that matches the regular expression. Therefore, the function will return ‘Y’.

xp_regex_search

The xp_regex_search extended procedure allows you to search for and retrieve all matches of a regular expression within a search string. It takes the same parameters as fn_regex_match, but instead of returning a single result, it returns a table with three columns: MatchNum, GroupNum, and MatchText.

Here’s an example usage of xp_regex_search:

EXEC dbo.xp_regex_search '[A-Z]+', 'George,Harold', 'I+'

In this example, the regular expression ‘[A-Z]+’ matches one or more uppercase letters, and the search string ‘George,Harold’ contains two patterns that match the regular expression. The extended procedure will return two rows: 1,1,’George’ and 2,1,’Harold’.

xp_regex_split

The xp_regex_split extended procedure allows you to split a search string into tokens based on a regular expression. It takes the same parameters as xp_regex_search and returns a table with two columns: TokenNum and TokenText.

Here’s an example usage of xp_regex_split:

EXEC dbo.xp_regex_split '\s+', 'One Two Three', NULL

In this example, the regular expression ‘\s+’ matches one or more whitespace characters, and the search string ‘One Two Three’ is split into three tokens: 1,’One’; 2,’Two’; and 3,’Three’.

fn_regex_replace

The fn_regex_replace function allows you to replace all occurrences of a regular expression in a search string with a specified replacement string. It takes the same parameters as fn_regex_match and returns the modified search string.

Here’s an example usage of fn_regex_replace:

SELECT dbo.fn_regex_replace ('\s', 'Hello There How Are You?', '.', 'I+')

In this example, the regular expression ‘\s’ matches whitespace characters, and the search string ‘Hello There How Are You?’ is modified to ‘Hello.There.How.Are.You?’ by replacing all whitespace characters with periods.

Summary

In this article, we explored the regular expression tools available in SQL Server. We discussed the fn_regex_match function for matching patterns, the xp_regex_search extended procedure for retrieving all matches, the xp_regex_split extended procedure for splitting strings, and the fn_regex_replace function for replacing patterns. Regular expressions are a powerful tool for text processing in SQL Server, and these tools can greatly enhance your database and application development.

Feel free to download the SQL 2000 DBA Toolkit and try out these regular expression tools in your own projects. If you find them useful, let us know which ones you use and how you use them. Happy coding!

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