MySQL :: MySQL 8.0 Reference Manual :: 26.4.29 The INFORMATION_SCHEMA INNODB_VIRTUAL Table

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MySQL 8.0 Reference Manual/.../ 的INFORMATION_SCHEMANODB_VIRTUAL Table

26.4.29 The INFORMATION_SCHEMA INNODB_VIRTUAL Table

TheINNODB_VIRTUALtable provides metadata aboutInnoDB虚拟生成列sand columns upon which virtual generated columns are based.

A row appears in theINNODB_VIRTUALtable for each column upon which a virtual generated column is based.

TheINNODB_VIRTUALtable has these columns:

TABLE_ID
An identifier representing the table associated with the virtual column; the same value asINNODB_TABLES.TABLE_ID.
POS
The position value of the虚拟生成列. The value is large because it encodes the column sequence number and ordinal position. The formula used to calculate the value uses a bitwise operation:
```
((nth virtual generated column for the InnoDB instance + 1) << 16) + the ordinal position of the virtual generated column
```
For example, if the first virtual generated column in theInnoDBinstance is the third column of the table, the formula is(0 + 1) << 16) + 2. The first virtual generated column in theInnoDBinstance is always number 0. As the third column in the table, the ordinal position of the virtual generated column is 2. Ordinal positions are counted from 0.
BASE_POS
The ordinal position of the columns upon which a virtual generated column is based.

Example

mysql> CREATE TABLE `t1` ( `a` int(11) DEFAULT NULL, `b` int(11) DEFAULT NULL, `c` int(11) GENERATED ALWAYS AS (a+b) VIRTUAL, `h` varchar(10) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4; mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_VIRTUAL WHERE TABLE_ID IN (SELECT TABLE_ID FROM INFORMATION_SCHEMA.INNODB_TABLES WHERE NAME LIKE "test/t1"); +----------+-------+----------+ | TABLE_ID | POS | BASE_POS | +----------+-------+----------+ | 98 | 65538 | 0 | | 98 | 65538 | 1 | +----------+-------+----------+

Notes

If a constant value is assigned to a虚拟生成列, as in the following table, an entry for the column does not appear in theINNODB_VIRTUALtable. For an entry to appear, a virtual generated column must have a base column.
```
CREATE TABLE `t1` ( `a` int(11) DEFAULT NULL, `b` int(11) DEFAULT NULL, `c` int(11) GENERATED ALWAYS AS (5) VIRTUAL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
```
However, metadata for such a column does appear in theINNODB_COLUMNStable.
你必须有PROCESSprivilege to query this table.
Use theINFORMATION_SCHEMACOLUMNStable or theSHOW COLUMNSstatement to view additional information about the columns of this table, including data types and default values.

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