## 15.23 InnoDB Restrictions and Limitations

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 This section describes restrictions and limitations of the `InnoDB` storage engine.

* You cannot create a table with a column name that matches the name of an internal `InnoDB` column (including `DB_ROW_ID`, `DB_TRX_ID`, and `DB_ROLL_PTR`. This restriction applies to use of the names in any lettercase.

  ```
  mysql> CREATE TABLE t1 (c1 INT, db_row_id INT) ENGINE=INNODB;
  ERROR 1166 (42000): Incorrect column name 'db_row_id'
  ```

* [`SHOW TABLE STATUS`](show-table-status.html) does not provide accurate statistics for `InnoDB` tables except for the physical size reserved by the table. The row count is only a rough estimate used in SQL optimization.

* `InnoDB` does not keep an internal count of rows in a table because concurrent transactions might “see” different numbers of rows at the same time. Consequently, `SELECT COUNT(*)` statements only count rows visible to the current transaction.

   For information about how `InnoDB` processes `SELECT COUNT(*)` statements, refer to the [`COUNT()`](aggregate-functions.html#function_count) description in [Section 12.20.1, “Aggregate Function Descriptions”](aggregate-functions.html).

* `ROW_FORMAT=COMPRESSED` is unsupported for page sizes greater than 16KB.

* A MySQL instance using a particular `InnoDB` page size ([`innodb_page_size`](innodb-parameters.html#sysvar_innodb_page_size)) cannot use data files or log files from an instance that uses a different page size.

* For limitations associated with importing tables using the *Transportable Tablespaces* feature, see [Table Import Limitations](innodb-statistics-estimation.html).

* For limitations associated with online DDL, see [Section 15.12.8, “Online DDL Limitations”](innodb-online-ddl-limitations.html).

* For limitations associated with general tablespaces, see [General Tablespace Limitations](general-tablespaces.html#general-tablespaces-limitations).

* For limitations associated with data-at-rest encryption, see [Encryption Limitations](innodb-data-encryption.html#innodb-data-encryption-limitations).

