SQL Server IN Clause with Variables: How to Avoid Conversion Errors?

IN clause and declaring variables in SQL Server: Avoiding type conversion errors

In some cases, you may need to include multiple values ​​in an IN clause that are represented by declared variables. This technique allows these values ​​to be centrally managed within complex stored procedures, eliminating the need for repeated updates. However, there are some challenges when executing such queries.

Question:

The following code snippet shows an example of this problem:

<code class="language-sql">DECLARE @ExcludedList VARCHAR(MAX)

SET @ExcludedList = '3,4,22'

SELECT * FROM A WHERE Id NOT IN (@ExcludedList)</code>

Error: Conversion failed while converting varchar value to type int.

Error reason:

This error occurs because the query attempts to compare an integer column (Id) to a string variable (@ExcludedList) containing comma-separated values. The IN clause expects integers as input, while the declared variables contain strings.

Solution:

To overcome this challenge, consider using table variables instead of declaring variables. Table variables can dynamically store multiple values ​​in tabular format, making it easier to use them in IN clauses.

<code class="language-sql">DECLARE @your_list TABLE (list INT)
INSERT into @your_list (list)
VALUES (3),(4),(22)

SELECT * FROM A WHERE Id NOT IN (select list from @your_list)</code>

By using table variables, queries now accurately compare integers to integers, resolving conversion errors.

This approach provides greater flexibility and efficiency when handling multiple values ​​in the IN clause. It allows the list to be populated dynamically and centralizes the management of these values ​​in one location, making it easier to update or modify the list as needed.

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