What is SQL?

Most SQL looks like this…

SELECT * FROM table WHERE column = 'value'

But it can also look like this…

DECLARE @Sum INT
DECLARE @I INT
SET @Sum = 0
SET @I = 1
WHILE @I < 1000
BEGIN
    IF (@I % 3 = 0) OR (@I % 5 = 0)
        SET @Sum = @Sum + @I
    SET @I = @I + 1
END
PRINT @Sum

SQL is mostly about data -- creating, changing, and retrieving it, for example. When someone says, "I saved it to the database," there's often some sort of SQL involved. I first learned a version of SQL (mySQL) in the year 2000 for a side project in college using PHP to connect a web page to some statistics of some sort. Since then, it has been enormously useful and building reports, answering questions, and generally serving as the meat-and-potatoes backbone of data-oriented (read: almost all) software systems. There are several popular versions of SQL. For example, I'm most familiar with the Microsoft version, MS-SQL or T-SQL. MySQL is also popular, and I'm somewhat familiar with that, too. But the variants are largely similar, so most people who "know SQL" are familiar with at least one.