Using Variables with Multiple Values in the WHERE Clause SQL

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As a developer, it’s common to encounter scenarios where you need to filter data based on multiple values. In this article, we’ll explore how to use variables with multiple values as parameters in the WHERE clause of your SQL queries.

Introduction

SQL is a powerful language that allows us to manage and manipulate data in databases. However, when dealing with multiple values, the query can become complex and difficult to maintain. This is where variables come into play. In this article, we’ll discuss how to use variables with multiple values as parameters in the WHERE clause of your SQL queries.

Creating a Sample Table

To illustrate our point, let’s create a sample table called Product that contains information about products.

CREATE TABLE [dbo].[Product]
(
    [ProductKey] [int] IDENTITY(1,1) NOT NULL,
    [Productnr] [nvarchar](25) NULL,
    [Color] [nvarchar](15) NOT NULL
)

We’ll insert some sample data into the table.

INSERT INTO [dbo].[Product] ([Productnr], [Color])
VALUES ('45678', 'Red'),
       ('98765', 'Blue'),
       ('46547', 'Black')

Using a Variable with Multiple Values

Now that we have our sample table, let’s create a variable @Color that contains multiple values. We’ll assign it the value 'Red,Blue'.

DECLARE @Color varchar(50) = 'Red,Blue';

We want to write a query that filters rows where the [Color] column is either 'Red' or 'Blue'. However, when we try to use the IN operator with multiple values, it doesn’t work as expected.

Using STRING_SPLIT

The first solution we tried was using the STRING_SPLIT function. We used it to split the value of @Color into individual strings and then checked if any of those strings were in the [Color] column.

DECLARE @Color varchar(50) = 'Red,Blue';

SELECT *
FROM [dbo].[Product]
WHERE EXISTS (
    SELECT * 
    FROM STRING_SPLIT(@Color, ',') s
    WHERE [Color] IN (SELECT @Color FROM STRING_SPLIT(@Color, ',')))

However, this approach has a few issues. Firstly, it’s not necessary to use the STRING_SPLIT function in the subquery. Secondly, it’s inefficient because it’s scanning through the entire table for every row.

Using IN with Multiple Values

The correct way to achieve this is by using the IN operator with multiple values. We can do this by wrapping the value of @Color in a subquery that selects individual values from the split string.

DECLARE @Color varchar(50) = 'Red,Blue';

SELECT *
FROM [dbo].[Product] p 
WHERE p.Color IN (
    SELECT s.value 
    FROM STRING_SPLIT(@Color, ',') s)

In this revised query, we’re selecting each individual value from the split string using the s.value syntax. This allows us to check if any of those values match the [Color] column.

Conclusion

Using variables with multiple values as parameters in the WHERE clause SQL can be achieved through several methods. By understanding how to use the IN operator, we can write efficient and effective queries that filter data based on multiple values.

Best Practices

When working with multiple values in your SQL queries, make sure to follow these best practices:

• Use the IN operator instead of the LIKE operator for better performance.
• Wrap values in a subquery when using the IN operator with multiple values.
• Avoid using string manipulation functions like STRING_SPLIT unless necessary.

By following these guidelines, you can write more efficient and effective SQL queries that handle multiple values with ease.

Last modified on 2023-12-23