MySQL FIND_IN_SET() vs IN(): Why Does IN() Only Return the First Match with Comma-Separated IDs?

FIND_IN_SET() vs IN(): Understanding the Difference in MySQL

Question:

In MySQL, we have two tables: "orders" and "company." The "attachedCompanyIDs" column in "orders" stores a comma-separated list of IDs referencing rows in "company." When querying for company names associated with an order using FIND_IN_SET(), we get the expected results. However, using IN() instead returns only the first matching company. Why does this happen?

Answer:

The attachedCompanyIDs column is a scalar value of type VARCHAR. When using IN(), MySQL casts the string to an integer, truncating it at the first non-numeric character (i.e., a comma). This means that if attachedCompanyIDs contains multiple values, only the first one will be considered for the IN comparison.

解决方法：

Depending on your specific scenario, there are several workarounds for this issue:

1. Use ARRAY Types (PostgreSQL Only): PostgreSQL supports array data types, allowing you to store comma-separated lists as arrays. This enables you to use ANY() to correctly compare the values in attachedCompanyIDs with the companyID column.
2. Limited Value Lists: If the length of the comma-separated lists in attachedCompanyIDs is limited, you can use a series of UNION ALL queries to convert the string into multiple rows. This allows you to perform the IN comparison on each row separately.

Additional Considerations:

1. Performance Impact: The use of FIND_IN_SET() can potentially lead to performance issues, especially for large datasets. Using the alternative solutions mentioned above can improve performance in these scenarios.
2. Readability and Maintenance: The alternative solutions can be more complex and less readable than using FIND_IN_SET(). Carefully consider the trade-offs between performance and maintainability when making your choice.

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