Here is something that I recently found very useful. If you have a table in your MySQL database which you want to insert a record if it does not exist but update the row if it does. MySQL 5.x has a very neat piece of script to handle this with out any conditional statements.
When writing a console application using C# / .NET and you want to connect to a database, the connection string is typically stored in the app.config file.
I was writing a simple JQuery script which filters out table rows based on class name. When I used visibility:hidden; I noticed that when it was made visible again, the table looked slightly broken. To fix this instead of using visibility:hidden use visibility:collapse; and this keeps the table format correct when it is made visible again.