Replace in SQL Server: What Dev Needs to Know

Dev, if you’re working with SQL Server, you’re probably familiar with the REPLACE function. This handy function allows you to replace one string of text with another within a larger body of text. But did you know that there are several different ways to use the REPLACE function? In this article, we’ll explore them all and give you the information you need to use REPLACE effectively in your SQL Server queries.

What is REPLACE?

At its most basic level, REPLACE is a string function that allows you to replace one set of characters with another in a given string. Here’s the basic syntax:

For example, let’s say you have a string that looks like this:

SELECT 'The quick brown fox jumps over the lazy dog.' AS Sentence

If you wanted to replace the word “fox” with “cat”, you could use the REPLACE function like this:

SELECT REPLACE('The quick brown fox jumps over the lazy dog.', 'fox', 'cat') AS Sentence

The result would be:

The quick brown cat jumps over the lazy dog.

Replacing a Portion of a String

But what if you only want to replace a portion of the string, rather than the entire thing? In this case, you can use the STUFF function in conjunction with REPLACE.

The STUFF function allows you to replace a portion of a string with another string. Here’s the basic syntax:

So if we wanted to replace just the word “brown” with the word “red” in our sentence, we could use this query:

SELECT STUFF('The quick brown fox jumps over the lazy dog.', CHARINDEX('brown', 'The quick brown fox jumps over the lazy dog.'), LEN('brown'), 'red') AS Sentence

The result would be:

The quick red fox jumps over the lazy dog.

Replacing with a Null Value

Another useful feature of the REPLACE function is its ability to replace a string with a null value. This can come in handy when you need to remove certain characters or strings from a larger body of text.

To replace a string with a null value, simply pass an empty string (”) as the new_string parameter:

SELECT REPLACE('The quick brown fox jumps over the lazy dog.', 'brown', '') AS Sentence

The result would be:

The quickfox jumps over the lazy dog.

Replacing Multiple Strings

What if you need to replace multiple strings within a larger body of text? You could use a series of nested REPLACE functions, but that can quickly become unwieldy.

A better approach is to use a table-valued function to store the search and replace values, and then join that table to your source data using an OUTER APPLY statement.

Here’s an example:

SELECT s.ID, t.NewValue AS OriginalValue, t.OldValue AS ReplacedValue, REPLACE(s.Value, t.OldValue, t.NewValue) AS NewValueFROM SourceTable sOUTER APPLY (VALUES('brown', 'red'),('lazy', 'active')) AS t (OldValue, NewValue)

In this example, we’re joining our source data (stored in the SourceTable table) with a table-valued function that contains the search and replace values. We’re then using the REPLACE function to perform the actual replacement on the Value column.

Frequently Asked Questions

What is the difference between REPLACE and STUFF?

The REPLACE function replaces any occurrence of a given string with another given string in a larger body of text. The STUFF function replaces a portion of a string with another given string. So while both functions allow you to modify strings in SQL Server, they do so in different ways.

Can I use REPLACE to remove a portion of a string?

Yes, you can use REPLACE to remove a portion of a string by passing an empty string as the new_string parameter. For example, to remove the word “brown” from our sentence, you could use this query:

SELECT REPLACE('The quick brown fox jumps over the lazy dog.', 'brown', '') AS Sentence

The result would be:

The quickfox jumps over the lazy dog.

Can I use REPLACE to replace multiple strings at once?

Yes, you can use a series of nested REPLACE functions to replace multiple strings at once. However, a better approach is to use a table-valued function to store the search and replace values, and then join that table to your source data using an OUTER APPLY statement. See the “Replacing Multiple Strings” section above for an example.

Is there a limit to the size of the string I can pass to the REPLACE function?

In SQL Server 2019 and later, the maximum size of a string is 2 GB. In earlier versions of SQL Server, the maximum size of a string is 8000 bytes.

Can I use REPLACE on non-string data types?

No, the REPLACE function is designed to work with string data types only.

Conclusion

As you can see, the REPLACE function is a powerful tool for modifying strings in SQL Server. Whether you need to replace a single word or multiple strings at once, there are several different ways to use REPLACE that can help you achieve your goals. We hope this article has given you the information you need to use REPLACE effectively in your SQL Server queries.