结构体dtype_t

/* SQL data type struct */
typedef struct dtype_struct        dtype_t;

struct dtype_struct{
    unsigned    mtype:;    /*!< main data type */
    unsigned    prtype:;    /*!< precise type; MySQL data
                    type, charset code, flags to
                    indicate nullability,
                    signedness, whether this is a
                    binary string, whether this is
                    a true VARCHAR where MySQL
                    uses 2 bytes to store the length */

    /* the remaining fields do not affect alphabetical ordering: */

    unsigned    len:;        /*!< length; for MySQL data this
                    is field->pack_length(),
                    except that for a >= 5.0.3
                    type true VARCHAR this is the
                    maximum byte length of the
                    string data (in addition to
                    the string, MySQL uses 1 or 2
                    bytes to store the string length) */
#ifndef UNIV_HOTBACKUP
    unsigned    mbminmaxlen:;    /*!< minimum and maximum length of a
                    character, in bytes;
                    DATA_MBMINMAXLEN(mbminlen,mbmaxlen);
                    mbminlen=DATA_MBMINLEN(mbminmaxlen);
                    mbmaxlen=DATA_MBMINLEN(mbminmaxlen) */
#endif /* !UNIV_HOTBACKUP */
};