The size of each index block. By default this is 1024, but the value may be changed at compile time when MySQL is built from source. 

• Rec/key 

This is a statistical value used by the optimizer. It tells how many rows there are per value for this index. A unique index always has a value of 1. This may be updated after a table is loaded (or greatly changed) with myisamchk -a . If this is not updated at all, a default value of 30 is given. 

The last part of the output provides information about each column: 

• Field 

The column number. 

• Start 

The byte position of the column within table rows. 

• Length 

The length of the column in bytes. 

• Nullpos , Nullbit 

For columns that can be NULL , MyISAM  stores NULL  values as a flag in a byte. Depending on how many nullable columns there are, there can be one or more bytes used for this purpose. The Nullpos and Nullbit  values, if nonempty, indicate which byte and bit contains that flag indicating whether the column is NULL . 

The position and number of bytes used to store NULL  flags is shown in the line for field 1. This is why there are six Field  lines for the person  table even though it has only five columns. 

• Type 

The data type. The value may contain any of the following descriptors: 

• constant 

All rows have the same value. 

• no endspace 

Do not store endspace. 

• no endspace, not_always 

Do not store endspace and do not do endspace compression for all values. 

• no endspace, no empty 

Do not store endspace. Do not store empty values. 

• table-lookup 

The column was converted to an ENUM . 

• zerofill( N ) 

