How to Efficiently Convert a String to a List of Strings in SQL Server

Learn how to effectively split a string into a list of strings in SQL Server for use in dynamic SQL queries.
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Introduction

Working with SQL Server often involves handling different data types and manipulating them to suit your needs. One common scenario is when you have a string formatted as a list of column names—like 'col1, col2, col3'—and you want to convert this string into a format that can be directly used in SQL statements.

In this post, we'll explore how to convert a string to a list of strings in SQL Server, breaking down the methods step-by-step so you can easily implement them in your stored procedures.

The Problem

Imagine you have a stored procedure that uses a variable containing a list of column names, represented as a single string. For example, if you call your stored procedure like this:

[[See Video to Reveal this Text or Code Snippet]]

You need to split this string into individual components so that you can use it in a SQL statement like:

[[See Video to Reveal this Text or Code Snippet]]

How do you achieve this? Let's dive into the solutions.

Solution Overview

There are different methods to split a string in SQL Server, and the choice can depend on your SQL Server version and personal preference. We will cover two effective methods below.

Method # 1: Basic REPLACE

This method is simple and works for earlier versions of SQL Server.

[[See Video to Reveal this Text or Code Snippet]]

Explanation:

Variables: We're declaring the main variable @ input with the string that contains column names. We also specify @ separator, which indicates how the items are separated (in this case, it’s a comma followed by a space).

Quote Handling: We're using the CHAR(39) function to represent a single quote, which is necessary for our SQL statement.

REPLACE: This function replaces the separators with a format that encases each column name in single quotes.

Output:

The output will look like this:

[[See Video to Reveal this Text or Code Snippet]]

Method # 2: Using STRING_AGG (SQL Server 2017 and onwards)

If you're working with SQL Server 2017 or later, you can utilize the STRING_AGG function combined with STRING_SPLIT for a more streamlined approach.

[[See Video to Reveal this Text or Code Snippet]]

Explanation:

STRING_SPLIT: This built-in function splits the @ input string based on the provided delimiter (in this case, a comma).

TRIM: We use TRIM to remove any extra spaces around the column names.

STRING_AGG: This function aggregates the results back into a single string, with each item encased in single quotes.

Output:

The result will similarly yield:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Understanding how to convert strings to lists in SQL Server is crucial for dynamic SQL queries and improving database efficiency. Whether you opt for the basic replacement method or the newer STRING_AGG method depends on your SQL Server version and your personal preferences.

Now, you're equipped with the knowledge to seamlessly handle strings and use them effectively in your SQL operations. Happy querying!