RESTORE DATABASE dbTarget FROM DISK='backup file location' WITH REPLACE
Note that if dbSource and dbTarget have different logical names for data and log files, you'll need to use the MOVE option in the RESTORE command:RESTORE DATABASE dbTarget FROM DISK='backup file location' WITH REPLACE
, MOVE 'dbSource_Data' TO 'path to dbTarget MDF file'
, MOVE 'dbSource_Log' TO 'path to dbTarget LDF file'
Naturally it's a good idea to make a backup of dbTarget first, unless it's completely empty.