What does LAST_INSERT_ID() return when no AUTO_INCREMENT value has been generated during the current connection?

Solution (By Examveda Team)

This question is about MySQL's `LAST_INSERT_ID()` function, which is very helpful when working with AUTO_INCREMENT columns. An AUTO_INCREMENT column automatically assigns a unique, increasing number to each new row you insert.

The question asks what happens when you use `LAST_INSERT_ID()` but no new row with an AUTO_INCREMENT value has been added during your current database connection.

Here's the breakdown of the options:

Option A: -1
This is the correct answer. If no AUTO_INCREMENT value has been generated, `LAST_INSERT_ID()` returns -1 to indicate that there was no recent insertion using AUTO_INCREMENT.

Option B: 0
This is incorrect because 0 is usually a valid AUTO_INCREMENT value, so it wouldn't be used to indicate the absence of a generated value.

Option C: 1
This is incorrect because 1 is also a valid AUTO_INCREMENT value and wouldn't signal that no value was generated.

Option D: 2
This is incorrect for the same reason as options C and B. 2 could be a valid AUTO_INCREMENT value.

In summary, when no AUTO_INCREMENT value has been generated in your current connection, `LAST_INSERT_ID()` will return -1.