Before we go any further, we need to learn about a very powerful component of SQL server. The variable. If you have programmed in any programming language before, you already know what a variable is. If you haven’t, think of it as a sticky note that has space for you to write one thing. This sticky note has a predetermined lifespan, during which you can erase what it says and replace it with something else. You can ask to see what’s on the sticky note at any time, too.