How does LAST_INSERT_ID() behave with multiple-record INSERT statements?

LAST_INSERT_ID() Behavior with Multiple-Record INSERT Statements

INSERT statements can insert multiple records in a single operation, providing increased efficiency in database modifications. However, the behavior of LAST_INSERT_ID() in ilyen scenarios is distinct from its operation with single-record insertions.

As highlighted in the MySQL documentation, LAST_INSERT_ID() returns the value generated for only the first row inserted in a multiple-record INSERT statement. This behavior is designed to facilitate the reproduction of such statements on other servers, ensuring consistency even in distributed environments.

Example

Consider the following example:

INSERT INTO people (name,age)
VALUES ('William',25), ('Bart',15), ('Mary',12);

After executing this statement, LAST_INSERT_ID() will retrieve the generated value for the first row inserted ('William', 25). This is in contrast to the expected value of 3, which would correspond to the last row inserted.

Practical Implications

Understanding this behavior is crucial for properly handling generated values in code that utilizes multiple-record INSERT statements. It is not advisable to rely on LAST_INSERT_ID() to obtain the last inserted ID in such cases. Instead, alternative methods such as fetching the affected row count or explicitly specifying the auto-increment value should be considered for accurate record retrieval.

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