How to Handle Duplicate Keys in MySQL INSERT Statements?

Ignore or Update Duplicate Keys in MySQL

When attempting to insert data into a table that enforces a UNIQUE constraint on a specific field, such as "tag" in this case, encountering duplicate values can lead to errors. This question explores how to handle such situations, with a particular focus on ignoring duplicates.

The first example provided demonstrates an attempt to insert multiple values into the "table_tags" table, with the intention of ignoring any duplicate tags. However, using "INSERT INTO ... ON DUPLICATE KEY IGNORE" is not recommended, as it has the potential to ignore all errors, not just duplicate key violations.

Instead, the recommended solution is to use "INSERT INTO ... ON DUPLICATE KEY UPDATE tag=tag;" syntax. This approach allows you to explicitly specify what should happen in the event of a duplicate key violation, in this case simply updating the existing record with the same value.

Using this syntax ensures that duplicate keys are not ignored, but rather their existing values are maintained. The duplicate key is effectively ignored, but the query does not produce any errors, resulting in "Query OK, 0 rows affected" as expected.

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