This command swaps two Redis databases, so that immediately all the clients
connected to a given database will see the data of the other database, and the
other way around. Example:

    SWAPDB 0 1

This will swap database 0 with database 1. All the clients connected with
database 0 will immediately see the new data, exactly like all the clients
connected with database 1 will see the data that was formerly of database 0.

@return

@simple-string-reply: `OK` if `SWAPDB` was executed correctly.

@examples

```
SWAPDB 0 1
```