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

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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