When you stop and start the WSS Search Service in Central Administrator (Operations=>Services on server=>Windows SharePoint Services Search), you may get the following error:
Database_name contains user-defined schema. Databases must be empty before they can be used. Delete all of the tables, stored procedures and other objects or use a different database.
Follow below steps to fix this issue:
Step 1 – Stop SQL Server service.
Step 2 – Delete files WSS_Search_ Servername.mdf and WSS_Search_ Servername_log.LDF.
Step 3 – Start SQL Server service.
Step 4 – Restart the WSS Search Service again (Provide new name for search database, old database name might not work.)
Maheshkumar S Tiwari edited Original. Comment: Added Tag and minor edit