decreased row count after an alter table

I ran an alter table (increased index length on a varchar column from 5 to 10 characters) on a large table (several million)rows.

A show-table-status after the alter shows about 10% decreased row count. I spot-checked and it doesn’t seem like there is any actual data loss.

Wondering what could be happening?

Running Mysql 5.0.60, with InnoDB.

InnoDB’s row statistics are only approximate estimates, so it’s nothing to worry about.


Wondering why is that? And why would the number change (so dramatically) with an alter-table?