There may be several methods to delete the files on disk from within SQL Server. Please click here to read a very good article about using the FORFILES Command to Delete files. It is flexible command and may be modified according to any environment.
SQL Server logs are valuable way to analyze condition and activities on SQL Server. Activities may be related to logins, sessions, backups, permission errors etc. SSMS GUI provides way to read SQL Server logs however also there are powerful T-SQL alternates that provide facilities filters for dates, keywords and specific log files. Click here to read a very well written article about reading SQL Server logs through T-SQL. Also do not forget to read valuable comments under this article.
At my job i am often required to link a row with previous row for date comparison. It may be done conventionally by using cursors. Onwards to SQL Server 2005 we have common table expression (CTE) which can be used for linking a row with previous row. Here is an article on this logic by David McKinney.
While going through optimization processes of some tables, i came across a very helpful article to get insight in Index usage. This Article on MSSQLTips.com has various scripts for analysis of usage of Indexes.
Using REPLACE inside the UPDATE statement is simple yet powerful combination to modify a part of string based on any criteria. Please read following original article with examples.
Bill Graziano article on SQLTEam.com