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Jun 12, 2020
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update auto-random.md (#2811) #2822

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6 changes: 3 additions & 3 deletions auto-random.md
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Expand Up @@ -122,7 +122,7 @@ TiDB supports parsing the version comment syntax. See the following example:
{{< copyable "sql" >}}

```sql
create table t (a bigint primary key /*T!30100 auto_random */)
create table t (a bigint primary key /*T![auto_rand] auto_random */)
```

{{< copyable "sql" >}}
Expand All @@ -133,9 +133,9 @@ create table t (a bigint primary key auto_random)

The above two statements have the same meaning.

In the result of `show create table`, the `AUTO_RANDOM` attribute is commented out. This comment includes a version number (for example, `/*T!30100 auto_random */`). Here `30100` indicates that the `AUTO_RANDOM` attribute is introduced in v3.1.0. TiDB of a lower version ignores the `AUTO_RANDOM` attribute in the above comment.
In the result of `show create table`, the `AUTO_RANDOM` attribute is commented out. This comment includes an attribute identifier (for example, `/*T![auto_rand] auto_random */`). Here `auto_rand` represents the `AUTO_RANDOM` attribute. Only the version of TiDB that implements the feature corresponding to this identifier can parse the SQL statement fragment properly.

This attribute supports forward compatibility, namely, downgrade compatibility. TiDB earlier than v3.1.0 ignores the `AUTO_RANDOM` attribute of a table (with the above comment), so TiDB of earlier versions can also use the table with the attribute.
This attribute supports forward compatibility, namely, downgrade compatibility. TiDB of earlier versions that do not implement this feature ignore the `AUTO_RANDOM` attribute of a table (with the above comment) and can also use the table with the attribute.

## Restrictions

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