Variables. One of the cornerstones of most, if not all, programming languages. They save you time by not having to type the same crap over and over. They can be manipulated for your own gain. They can even be used in your MySQL queries.
The declaration syntax for variables in MySQL is a bit interesting, but not so outlandish that it’s not easy to remember:
SET @nameOfStringVariable := 'some string'; SET @nameOfNumberVariable := 12345;
With our variables set, you can reference them right in our queries:
SELECT column_1, column_2, column_3 FROM some_table WHERE some_column = @someVariable;
The variables can be used in comparison operators, or concatenated with results, all of the usual stuff.
Also, they make it easy to select a value, and assign it to a variable, so that you can use it in a subsequent query:
SELECT @someOtherValue := some_other_column FROM some_table WHERE some_column = @someVariable;
Keep in mind, that if your query returns multiple rows, the last row will be the one that’s value is assigned to the variable.