(mysql.info.gz) Storage requirements

 
 11.5 Column Type Storage Requirements
 =====================================
 
 The storage requirements for each of the column types supported by
 MySQL are listed by category.
 
 The maximum size of a row in a `MyISAM' table is 65,534 bytes. Each
 `BLOB' and `TEXT' column accounts for only five to nine bytes toward
 this size.
 
 If a `MyISAM' or `ISAM' table includes any variable-length column
 types, the record format will also be variable length.  When a table is
 created, MySQL may, under certain conditions, change a column from a
 variable-length type to a fixed-length type or vice versa.  
 Silent column changes.
 
 Storage Requirements for Numeric Types
 --------------------------------------
 
 *Column Type*                 *Storage Required*
 `TINYINT'                     1 byte
 `SMALLINT'                    2 bytes
 `MEDIUMINT'                   3 bytes
 `INT', `INTEGER'              4 bytes
 `BIGINT'                      8 bytes
 `FLOAT(P)'                    4 bytes if 0 <= P <= 24, 8 bytes if 25 <=
                               P <= 53
 `FLOAT'                       4 bytes
 `DOUBLE [PRECISION]', item    8 bytes
 `REAL'                        
 `DECIMAL(M,D)',               M+2 bytes if D > 0, `M+1' bytes if D = 0
 `NUMERIC(M,D)'                (D+2, if `M < D')
 
 Storage Requirements for Date and Time Types
 --------------------------------------------
 
 *Column Type*                 *Storage Required*
 `DATE'                        3 bytes
 `DATETIME'                    8 bytes
 `TIMESTAMP'                   4 bytes
 `TIME'                        3 bytes
 `YEAR'                        1 byte
 
 Storage Requirements for String Types
 -------------------------------------
 
 *Column Type*                 *Storage Required*
 `CHAR(M)'                     `M' bytes, 0 `<= M <=' 255
 `VARCHAR(M)'                  L+1 bytes, where `L <= M' and 0 `<= M <='
                               255
 `TINYBLOB', `TINYTEXT'        L+1 bytes, where L < 2^8
 `BLOB', `TEXT'                L+2 bytes, where L < 2^16
 `MEDIUMBLOB', `MEDIUMTEXT'    L+3 bytes, where L < 2^24
 `LONGBLOB', `LONGTEXT'        L+4 bytes, where L < 2^32
 `ENUM('VALUE1','VALUE2',...)' 1 or 2 bytes, depending on the number of
                               enumeration values (65,535 values maximum)
 `SET('VALUE1','VALUE2',...)'  1, 2, 3, 4, or 8 bytes, depending on the
                               number of set members (64 members maximum)
 
 `VARCHAR' and the `BLOB' and `TEXT' types are variable-length types.
 For each, the storage requirements depend on the actual length of
 column values (represented by L in the preceding table), rather than on
 the type's maximum possible size.  For example, a `VARCHAR(10)' column
 can hold a string with a maximum length of 10 characters.  The actual
 storage required is the length of the string (L), plus 1 byte to record
 the length of the string.  For the string `'abcd'', L is 4 and the
 storage requirement is 5 bytes.
 
 The `BLOB' and `TEXT' types require 1, 2, 3, or 4 bytes to record the
 length of the column value, depending on the maximum possible length of
 the type.   `BLOB' BLOB.
 
 The size of an `ENUM' object is determined by the number of different
 enumeration values.  One byte is used for enumerations with up to 255
 possible values.  Two bytes are used for enumerations with up to 65,535
 values.  `ENUM' ENUM.
 
 The size of a `SET' object is determined by the number of different set
 members.  If the set size is N, the object occupies `(N+7)/8' bytes,
 rounded up to 1, 2, 3, 4, or 8 bytes.  A `SET' can have a maximum of 64
 members.  `SET' SET.
Info Catalog
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