Which command is not used to configure VLAN on a switch?

The command associated with configuring VLANs on a switch is not "router vlan." This option does not relate to the VLAN configuration process on switches. Instead, it incorrectly suggests that VLANs can be configured directly on a router using this command, which is not the case.

In contrast, the other options are indeed involved in VLAN configuration. The "vlan database" command is used in older Cisco switches to enter VLAN configuration mode and create or modify VLANs. The "switchport mode access" command is critical for setting a port to operate in access mode, which allows it to belong to a single VLAN. Additionally, the "switchport access vlan" command is used to assign a specific VLAN to a switch port, enabling the traffic from that port to be tagged with the specified VLAN ID.

Thus, "router vlan" does not fit into the VLAN configuration context for switches, making it the right choice as the command not used for this purpose.