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InnoDB tables should always include 2 or 3 system columns, appended to the end of the column list: DB_ROW_ID, DB_TRX_ID, DB_ROLL_PTR. I do not remember it for sure, but it may be that these columns are always present in the internal representation. In that case, this would not be a bug.
Not to be confused with the columns of the table are the fields of indexes. There always is a "clustered index", which actually used to refer to a never-implemented feature that the clustered index would contain records from multiple tables, possibly each one carrying a similar PRIMARY KEY.
The "clustered index" refers to the index where the data is stored, along with the undo log information. Its key normally is the primary key (which can also be UNIQUE INDEX on NOT NULL columns). If no primary key has been defined, then the clustered index will be called GEN_CLUST_INDEX(DB_ROW_ID).
For the tables in the Description, the clustered index fields should be as follows:
| table |
clustered index fields |
| t |
DB_ROW_ID,DB_TRX_ID,DB_ROLL_PTR,i |
| t1 |
i,DB_TRX_ID,DB_ROLL_PTR |
You can think that the DB_ROW_ID is only "materialized" in the indexes if there is no primary key or unique index on NOT NULL columns. It is a special kind of a hidden virtual column.
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