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28.4.9 INFORMATION_SCHEMA INNODB_COLUMNS 表

The INNODB_COLUMNS table provides metadata about InnoDB table columns.

For related usage information and examples, see Section 17.15.3, “InnoDB INFORMATION_SCHEMA Schema Object Tables”.

The INNODB_COLUMNS table has these columns:

TABLE_ID

An identifier representing the table associated with the column; the same value as INNODB_TABLES.TABLE_ID.
NAME

The name of the column. These names can be uppercase or lowercase depending on the lower_case_table_names setting. There are no special system-reserved names for columns.
POS

The ordinal position of the column within the table, starting from 0 and incrementing sequentially. When a column is dropped, the remaining columns are reordered so that the sequence has no gaps. The POS value for a virtual generated column encodes the column sequence number and ordinal position of the column. For more information, see the POS column description in Section 28.4.29, “The INFORMATION_SCHEMA INNODB_VIRTUAL Table”.
MTYPE

Stands for “main type”. A numeric identifier for the column type. 1 = VARCHAR, 2 = CHAR, 3 = FIXBINARY, 4 = BINARY, 5 = BLOB, 6 = INT, 7 = SYS_CHILD, 8 = SYS, 9 = FLOAT, 10 = DOUBLE, 11 = DECIMAL, 12 = VARMYSQL, 13 = MYSQL, 14 = GEOMETRY.
PRTYPE

The InnoDB “precise type”, a binary value with bits representing MySQL data type, character set code, and nullability.
LEN

The column length, for example 4 for INT and 8 for BIGINT. For character columns in multibyte character sets, this length value is the maximum length in bytes needed to represent a definition such as VARCHAR(N); that is, it might be 2*N, 3*N, and so on depending on the character encoding.
HAS_DEFAULT

A boolean value indicating whether a column that was added instantly using ALTER TABLE ... ADD COLUMN with ALGORITHM=INSTANT has a default value. All columns added instantly have a default value, which makes this column an indicator of whether the column was added instantly.
DEFAULT_VALUE

The initial default value of a column that was added instantly using ALTER TABLE ... ADD COLUMN with ALGORITHM=INSTANT. If the default value is NULL or was not specified, this column reports NULL. An explicitly specified non-NULL default value is shown in an internal binary format. Subsequent modifications of the column default value do not change the value reported by this column.

mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_COLUMNS where TABLE_ID = 71\G
*************************** 1. row ***************************
     TABLE_ID: 71
         NAME: col1
          POS: 0
        MTYPE: 6
       PRTYPE: 1027
          LEN: 4
  HAS_DEFAULT: 0
DEFAULT_VALUE: NULL
*************************** 2. row ***************************
     TABLE_ID: 71
         NAME: col2
          POS: 1
        MTYPE: 2
       PRTYPE: 524542
          LEN: 10
  HAS_DEFAULT: 0
DEFAULT_VALUE: NULL
*************************** 3. row ***************************
     TABLE_ID: 71
         NAME: col3
          POS: 2
        MTYPE: 1
       PRTYPE: 524303
          LEN: 10
  HAS_DEFAULT: 0
DEFAULT_VALUE: NULL

You must have the PROCESS privilege to query this table.
Use the INFORMATION_SCHEMA COLUMNS table or the SHOW COLUMNS statement to view additional information about the columns of this table, including data types and default values.

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