• MIN_ROWS 

The minimum number of rows you plan to store in the table. The MEMORY  storage engine uses this option as a hint about memory use. 

• PACK_KEYS 

Takes effect only with MyISAM  tables. Set this option to 1 if you want to have smaller indexes. This usually makes updates slower and reads faster. Setting the option to 0 disables all packing of keys. Setting it to DEFAULT  tells the storage engine to pack only long CHAR , VARCHAR , BINARY , or VARBINARY  columns. 

If you do not use PACK_KEYS , the default is to pack strings, but not numbers. If you use PACK_KEYS=1 , numbers are packed as well. 

When packing binary number keys, MySQL uses prefix compression: 

•Every key needs one extra byte to indicate how many bytes of the previous key are the same for the next key. 

•The pointer to the row is stored in high-byte-first order directly after the key, to improve compression. 

This means that if you have many equal keys on two consecutive rows, all following “same”  keys usually only take two bytes (including the pointer to the row). Compare this to the ordinary case where the following keys takes storage_size_for_key + pointer_size  (where the pointer size is usually 4). Conversely, you get a significant benefit from prefix compression only if you have many numbers that are the same. If all keys are totally different, you use one byte more per key, if the key is not a key that can have NULL  values. (In this case, the packed key length is stored in the same byte that is used to mark if a key is NULL .) 

• PASSWORD 

This option is unused. 

• ROW_FORMAT 

Defines the physical format in which the rows are stored. 

When creating a table with strict mode disabled, the storage engine’s default row format is used if the specified row format is not supported. The actual row format of the table is reported in the Row_format column in response to SHOW TABLE STATUS . The Create_options  column shows the row format that was specified in the CREATE TABLE  statement, as does SHOW CREATE TABLE . 

Row format choices differ depending on the storage engine used for the table. 

For InnoDB  tables: 

•The default row format is defined by innodb_default_row_format , which has a default setting of DYNAMIC . The default row format is used when the ROW_FORMAT  option is not defined or when ROW_FORMAT=DEFAULT  is used. 

If the ROW_FORMAT  option is not defined, or if ROW_FORMAT=DEFAULT  is used, operations that rebuild a table also silently change the row format of the table to the default defined by innodb_default_row_format . For more information, see Defining the Row Format of a Table. 

•For more efficient InnoDB  storage of data types, especially BLOB  types, use the DYNAMIC . See DYNAMIC Row Format for requirements associated with the DYNAMIC  row format. 

