SHOW Statements For  InnoDB  tables, the row count is only a rough estimate used in SQL optimization. (This is also true if the  InnoDB  table is partitioned.) The average row length. For  MyISAM ,  Data_length  is the length of the data file, in bytes. For  InnoDB ,  Data_length  is the approximate amount of space allocated for the clustered index, in bytes. Specifically, it is the clustered index size, in pages, multiplied by the  InnoDB  page size. Refer to the notes at the end of this section for information regarding other storage engines. For  MyISAM ,  Max_data_length  is maximum length of the data file. This is the total number of bytes of data that can be stored in the table, given the data pointer size used. Unused for  InnoDB . Refer to the notes at the end of this section for information regarding other storage engines. For  MyISAM ,  Index_length  is the length of the index file, in bytes. For  InnoDB ,  Index_length  is the approximate amount of space allocated for non-clustered indexes, in bytes. Specifically, it is the sum of non-clustered index sizes, in pages, multiplied by the  InnoDB  page size. Refer to the notes at the end of this section for information regarding other storage engines. The number of allocated but unused bytes. InnoDB  tables report the free space of the tablespace to which the table belongs. For a table located in the shared tablespace, this is the free space of the shared tablespace. If you are using multiple tablespaces and the table has its own tablespace, the free space is for only that table. Free space means the number of bytes in completely free extents minus a safety margin. Even if free space displays as 0, it may be possible to insert rows as long as new extents need not be allocated. For NDB Cluster,  Data_free  shows the space allocated on disk for, but not used by, a Disk Data table or fragment on disk. (In-memory data resource usage is reported by the  Data_length  column.) For partitioned tables, this value is only an estimate and may not be absolutely correct. A more accurate method of obtaining this information in such cases is to query the  INFORMATION_SCHEMA PARTITIONS table, as shown in this example: For more information, see Section 26.3.21, “The INFORMATION_SCHEMA PARTITIONS Table” . 2960 SELECT SUM(DATA_FREE) FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_SCHEMA = ’mydb’ AND TABLE_NAME = ’mytable’; • Avg_row_length • Data_length • Max_data_length • Index_length • Data_free