For example, if
t1 is currently not an InnoDB table, this statement changes its storage engine to InnoDB:
ALTER TABLE t1 ENGINE = InnoDB;
If the table is already InnoDB, this will rebuild the table and its indexes and have an effect similar to
OPTIMIZE TABLE. You may gain some disk space improvement.
If the value of
innodb_file_per_table is currently different than the value in effect when
t1 was built, this will convert to (or from) file_per_table.