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merged 4 commits into from
Jun 18, 2020
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combine duplicate doc #2934

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combine duplicate doc
tangenta Jun 17, 2020
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Merge branch 'master' into combine_show_rowid
yikeke Jun 17, 2020
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yikeke Jun 18, 2020
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Merge branch 'master' into combine_show_rowid
ti-srebot Jun 18, 2020
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20 changes: 15 additions & 5 deletions sql-statements/sql-statement-show-table-next-rowid.md
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Expand Up @@ -6,10 +6,12 @@ category: reference

# SHOW TABLE NEXT_ROW_ID

`SHOW TABLE NEXT_ROW_ID` can be used to show the implicitly allocated global Row ID of a table.
`SHOW TABLE NEXT_ROW_ID` is used to show the details of some special columns of a table, including:

- For most of the tables, TiDB allocates a unique number for each record. The max allocated ID is persisted in the storage layer. Each TiDB server applies for a range of IDs on demand and caches them for ID allocation. This syntax can be used to query the next value to allocate, recorded in the storage layer.
- For the tables with integer primary key for optimization, TiDB maps the values in the primary key column to Row ID. Thus, `SHOW TABLE NEXT_ROW_ID` is meaningless for these tables.
* `AUTO_INCREMENT` column automatically created by TiDB, namely, `_tidb_rowid` column.
* `AUTO_INCREMENT` column created by users.
* [`AUTO_RANDOM`](/auto-random.md) column created by users.
* [`SEQUENCE`](/sql-statements/sql-statement-create-sequence.md) created by users.

## Synopsis

Expand All @@ -23,6 +25,8 @@ category: reference

## Examples

For newly created tables, `NEXT_GLOBAL_ROW_ID` is `1` because no Row ID is allocated.

{{< copyable "sql" >}}

```sql
Expand All @@ -31,7 +35,6 @@ Query OK, 0 rows affected (0.06 sec)
```

```sql
# For newly created tables, NEXT_GLOBAL_ROW_ID is 1 because no Row ID is allocated.
show table t next_row_id;
+---------+------------+-------------+--------------------+
| DB_NAME | TABLE_NAME | COLUMN_NAME | NEXT_GLOBAL_ROW_ID |
Expand All @@ -41,6 +44,8 @@ show table t next_row_id;
1 row in set (0.00 sec)
```

Data have been written to the table. The TiDB server that inserts the data allocates and caches 30000 IDs at once. Thus, NEXT_GLOBAL_ROW_ID is 30001 now.

```sql
insert into t values (), (), ();
Query OK, 3 rows affected (0.02 sec)
Expand All @@ -49,7 +54,6 @@ Records: 3 Duplicates: 0 Warnings: 0

```sql
show table t next_row_id;
# Data have been written to the table. The TiDB server that inserts the data allocates and caches 30000 IDs at once. Thus, NEXT_GLOBAL_ROW_ID is 30001 now.
+---------+------------+-------------+--------------------+
| DB_NAME | TABLE_NAME | COLUMN_NAME | NEXT_GLOBAL_ROW_ID |
+---------+------------+-------------+--------------------+
Expand All @@ -61,3 +65,9 @@ show table t next_row_id;
## MySQL compatibility

`SHOW TABLE NEXT_ROW_ID` is specific to TiDB.

## See also

* [CREATE TABLE](/sql-statements/sql-statement-create-table.md)
* [AUTO_RANDOM](/auto-random.md)
* [CREATE_SEQUENCE](/sql-statements/sql-statement-create-sequence.md)