How to restore content database using SQL server in SharePoint 2010 ?

1. If the Windows SharePoint Services Timer service is running, stop the service and wait for several minutes for any currently running stored procedures to finish.
2. Do not restart the service until after you restore the content databases.
3. Open SQL Server Management Studio
4. Connect to the database server.
5. Right-click the Database that you want to restore > Tasks > Restore > Database.
6. In the Restore Database dialog box, specify the destination and the source, and then select the backup set or sets that you want to restore.
7. In the Select a page pane, click Options.
8. In the Restore options section, select only Overwrite the existing database.
9. In the Recovery state section:
• If you have included all the transaction logs that you must restore, select RECOVER WITH RECOVERY.
• If you must restore additional transaction logs, select RECOVER WITH NORECOVERY.
• The third option, RECOVER WITH STANDBY is not used in this scenario.
10. Click OK to complete the recovery operation.
11. Repeat steps 4 through 10 for each database that you are restoring.
12. Start the Windows SharePoint Services Timer service.

Ref: http://technet.microsoft.com/en-us/library/ee748604#section3