The number of integer columns that do not occupy the full byte range of their type. These are changed to a smaller type. For example, a BIGINT  column (eight bytes) can be stored as a TINYINT  column (one byte) if all its values are in the range from -128  to 127 . 

• pre-space 

The number of decimal columns that are stored with leading spaces. In this case, each value contains a count for the number of leading spaces. 

• end-space 

The number of columns that have a lot of trailing spaces. In this case, each value contains a count for the number of trailing spaces. 

• table-lookup 

The column had only a small number of different values, which were converted to an ENUM  before Huffman compression. 

• zero 

The number of columns for which all values are zero. 

• Original trees 

The initial number of Huffman trees. 

• After join 

The number of distinct Huffman trees left after joining trees to save some header space. 

After a table has been compressed, the Field  lines displayed by myisamchk -dvv  include additional information about each column: 

• 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 . 

