Why Doesn't MySQL WHERE IN () Return Multiple ID Matches When Using SET Data Type?

MySQL WHERE IN () Not Returning Multiple ID Matches

In MySQL, the WHERE IN () clause is used to filter results based on a specified list of values. However, when a table column contains multiple values, it may not return rows that match all of the specified values.

Consider the following query:

SELECT * FROM table WHERE id IN (1, 2, 3, 4);

This query retrieves all rows where the id column is equal to 1, 2, 3, or 4. However, if a row contains more than one of these values, it may not be returned.

To understand why, it's important to note that the IN clause translates to a logical OR condition:

SELECT * FROM table WHERE id='1' OR id='2' OR id='3' OR id='4';

This means that only rows that match exactly one of the specified values will be returned.

Solution Using SET Data Type and FIND_IN_SET

One way to resolve this issue is to change the data type of the id column to a SET data type. In a SET column, multiple values can be stored as a comma-separated list.

Once the data type is changed to SET, you can use the FIND_IN_SET function to retrieve rows based on a specific value:

SELECT * FROM table WHERE FIND_IN_SET('1', id);

This query will return all rows where the id column contains the value 1, regardless of whether it contains other values as well.

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