# Nonclustered Index


![`smart`](NonclusteredIndex02_aa_003_20230922.png)

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In the this slide, we can see that for each row in the TiDB database table, a RowID (also known as _tidb_rowid) is assigned. This RowID ensures the uniqueness of each row within the table and can be used as a key to locate each row. You can also understand that TiDB database does not consider whether your table has a primary key, but adds a unique indexed column called RowID to your table.

It should be noted that in the TiDB database, the RowID type of a Nonclustered Index Table is a 64-bit signed integer (BIGINT). Each row of data has a unique RowID that is used to locate and access the corresponding data in the underlying storage engine. RowID is a hidden column in TiDB and can be viewed through the SHOW COLUMNS command. It is important to note that RowID is automatically generated and managed by TiDB and cannot be directly modified or manipulated manually.