add limit to import into (#18875) (#18879)

sql-statements/sql-statement-import-into.md

@@ -21,6 +21,7 @@ The `IMPORT INTO` statement lets you import data to TiDB via the [Physical Impor
 ## Restrictions
 
 - `IMPORT INTO` only supports importing data into existing empty tables in the database.
+- `IMPORT INTO` does not support importing data into a [temporary table](/temporary-tables.md) or a [cached table](/cached-tables.md).
 - `IMPORT INTO` does not support transactions or rollback. Executing `IMPORT INTO` within an explicit transaction (`BEGIN`/`END`) will return an error.
 - `IMPORT INTO` does not support working simultaneously with features such as [Backup & Restore](https://docs.pingcap.com/tidb/stable/backup-and-restore-overview), [`FLASHBACK CLUSTER`](/sql-statements/sql-statement-flashback-cluster.md), [acceleration of adding indexes](/system-variables.md#tidb_ddl_enable_fast_reorg-new-in-v630), data import using TiDB Lightning, data replication using TiCDC, or [Point-in-Time Recovery (PITR)](https://docs.pingcap.com/tidb/stable/br-log-architecture). For more compatibility information, see [Compatibility of TiDB Lightning and `IMPORT INTO` with TiCDC and Log Backup](https://docs.pingcap.com/tidb/stable/tidb-lightning-compatibility-and-scenarios).
 - During the data import process, do not perform DDL or DML operations on the target table, and do not execute [`FLASHBACK DATABASE`](/sql-statements/sql-statement-flashback-database.md) for the target database. These operations can lead to import failures or data inconsistencies. In addition, it is **NOT** recommended to perform read operations during the import process, as the data being read might be inconsistent. Perform read and write operations only after the import is completed.