MySQL frm 文件详解

 1CREATE TABLE `t_create_bit_enum_set` (
 2  `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增主键',
 3  `i1` INT(10) UNSIGNED NOT NULL DEFAULT '0' COMMENT '整数1',
 4  `city` ENUM('北京','上海','广州','深圳','天津','重庆') DEFAULT NULL COMMENT '城市',
 5  `color` SET('红','橙','黄','绿','青','蓝','紫') DEFAULT '蓝' COMMENT '颜色',
 6  `str1` VARCHAR(255) DEFAULT NULL COMMENT '字符串1',
 7  `str2` VARCHAR(64) NOT NULL DEFAULT '' COMMENT '字符串3',
 8  `str3` CHAR(20) DEFAULT NULL COMMENT '字符串4',
 9  `status` BIT(1) NOT NULL DEFAULT b'1' COMMENT '状态',
10  PRIMARY KEY (`id`) COMMENT '主键索引',
11  KEY `idx_str2_i1` (`str2`, `i1`) KEY_BLOCK_SIZE=1024 COMMENT 'str2_i1索引'
12) ENGINE=INNODB DEFAULT CHARSET=utf8 MIN_ROWS=1 MAX_ROWS=100000 COMMENT='带enum/set/bit字段的表';

 1// sql/unireg.cc
 2static uint pack_keys(uchar *keybuff, uint key_count, KEY *keyinfo,
 3                      ulong data_offset)
 4  // ...... 此处省略 N 行
 5
 6  // 如果表中索引数量或者索引字段数量大于 127 个
 7  if (key_count > 127 || key_parts > 127)
 8  {
 9    // keybuff[0] = Offset 4096
10    // 存储的值为：索引数量 + 128，其中 128 是个标志位，在读取 frm 文件的时候会用到
11    keybuff[0]= (key_count & 0x7f) | 0x80;
12
13    // keybuf[1] = Offset 4097
14    // 存储的值为：索引数量 - 128
15    keybuff[1]= key_count >> 7;
16
17    // keybuf[2 ~ 3] = Offset 4098 ~ 4099
18    // 存储的值为：索引字段数量
19    int2store(keybuff+2,key_parts);
20  }
21  else // 表中索引字段数量小于等于 127
22  {
23    // keybuf[0] = Offset 4096，存储的值为：索引数量
24    keybuff[0]=(uchar) key_count;
25    
26    // keybuf[1] = Offset 4097，存储的值为：索引中字段数量
27    keybuff[1]=(uchar) key_parts;
28    
29    // keybuf[2 ~ 3] = Offset[4098 ~ 4099]，存储的值为 null
30    keybuff[2]= keybuff[3]= 0;
31  }
32
33  // ...... 此处省略 N 行
34}

 1// sql/unireg.cc
 2static bool make_empty_rec(THD *thd, File file,
 3			   uint table_options,
 4			   List<Create_field> &create_fields,
 5			   uint reclength,
 6                           ulong data_offset,
 7                           handler *handler)
 8{
 9    // ...... 此处省略 N 行代码
10
11  /*
12    We need to set the unused bits to 1. If the number of bits is a multiple
13    of 8 there are no unused bits.
14  */
15  if (null_count & 7)
16    *(null_pos + null_count / 8)|= ~(((uchar) 1 << (null_count & 7)) - 1);
17
18    // ...... 此处省略 N 行代码
19}

 1// sql/field.h:671
 2/* 
 3We use three additional unireg types for TIMESTAMP to overcome limitation 
 4of current binary format of .frm file. We'd like to be able to support 
 5NOW() as default and on update value for such fields but unable to hold 
 6this info anywhere except unireg_check field. This issue will be resolved
 7in more clean way with transition to new text based .frm format.
 8See also comment for Field_timestamp::Field_timestamp().
 9*/
10enum utype  { NONE,DATE,SHIELD,NOEMPTY,CASEUP,PNR,BGNR,PGNR,YES,NO,REL,
11	CHECK,EMPTY,UNKNOWN_FIELD,CASEDN,NEXT_NUMBER,INTERVAL_FIELD,
12            BIT_FIELD, TIMESTAMP_OLD_FIELD, CAPITALIZE, BLOB_FIELD,
13            TIMESTAMP_DN_FIELD, TIMESTAMP_UN_FIELD, TIMESTAMP_DNUN_FIELD,
14            GENERATED_FIELD= 128 };

 1// sql/binary_log_types.h:50
 2typedef enum enum_field_types {
 3  MYSQL_TYPE_DECIMAL, MYSQL_TYPE_TINY,
 4  MYSQL_TYPE_SHORT,  MYSQL_TYPE_LONG,
 5  MYSQL_TYPE_FLOAT,  MYSQL_TYPE_DOUBLE,
 6  MYSQL_TYPE_NULL,   MYSQL_TYPE_TIMESTAMP,
 7  MYSQL_TYPE_LONGLONG,MYSQL_TYPE_INT24,
 8  MYSQL_TYPE_DATE,   MYSQL_TYPE_TIME,
 9  MYSQL_TYPE_DATETIME, MYSQL_TYPE_YEAR,
10  MYSQL_TYPE_NEWDATE, MYSQL_TYPE_VARCHAR,
11  MYSQL_TYPE_BIT,
12  MYSQL_TYPE_TIMESTAMP2,
13  MYSQL_TYPE_DATETIME2,
14  MYSQL_TYPE_TIME2,
15  MYSQL_TYPE_JSON=245,
16  MYSQL_TYPE_NEWDECIMAL=246,
17  MYSQL_TYPE_ENUM=247,
18  MYSQL_TYPE_SET=248,
19  MYSQL_TYPE_TINY_BLOB=249,
20  MYSQL_TYPE_MEDIUM_BLOB=250,
21  MYSQL_TYPE_LONG_BLOB=251,
22  MYSQL_TYPE_BLOB=252,
23  MYSQL_TYPE_VAR_STRING=253,
24  MYSQL_TYPE_STRING=254,
25  MYSQL_TYPE_GEOMETRY=255
26} enum_field_types;