Why Doesn't My MySQL WHERE IN () Query Return Records with Multiple Values?

MySQL WHERE IN () Query Not Returning Expected Results

In MySQL, the WHERE IN () statement is commonly used to retrieve records based on a set of specified values. However, sometimes users encounter situations where expected rows are not returned in the results.

Problem Description:

A user has a query that selects all rows from the "table" table where the "id" column is in a specified list:

<code class="sql">SELECT * FROM table WHERE id IN (1,2,3,4);</code>

The user has noted that when a record has multiple "id" values (e.g., both 1 and 3), it is not returned in the results.

Understanding the Issue:

The WHERE IN () statement translates the provided list of values into a series of OR operators:

<code class="sql">SELECT * FROM table WHERE id='1' or id='2' or id='3' or id='4';</code>

This means that only rows where the "id" column matches exactly one of the specified values will be returned.

Solution 1: Using FIND_IN_SET

One approach to overcome this limitation is to modify the data structure by changing the "id" column's data type to SET. This allows the column to store multiple values.

Using the FIND_IN_SET function, you can then search for records where a specific value is present within the SET:

<code class="sql">SELECT * FROM table WHERE FIND_IN_SET('1', id);</code>

However, it's important to note that this solution incurs additional complexity and may not be suitable for all scenarios.

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