When deciding how to store your data in MySQL  you might see a few options. Especially if you look at float variations:

float

double

decimal
But which one should you use? What's the difference? Let's take a look at these fields and see where they can be used:
Our example database:
And here's the data we have stored in it:
Now, let's try to sum the total on each of these fields:
As you can see, it quickly shows us that float
is the least precise, while decimal
is the most precise. So, what's the use case of this?

float
anddouble
are good for calculations where you don't have to be really precise. These values will not always come up to an exact precision, but they are fast to calculate. 
decimal
is suitable for calculations where you need to be precise. These values will always come up to an exact precision, but they are slower to calculate.
That said, here's the typical use case for each of these fields that we have seen:
 Geo Coordinates 
double
, as you don't need to be really precise, but you need to be fast and store a lot of decimal places  Money 
decimal
, as you need to be precise, but you don't need to be fast. You can, and should store money in cents, but this is a backup idea  Statistics 
float/double
ordecimal
, as this depends on how precise you need to be. If you are okay being off by a few decimal places  usefloat
, if you need to be precise  usedecimal
.  Stock values (especially if products can be sold in measurements) 
decimal
, as you need to be precise.  Distance 
double
if you don't need to be precise,decimal
if you need to be precise. For example, you might be okay with being off by a few meters usingdouble
.  Measurements 
decimal
, as you need to be precise.  Percentages 
decimal
, as you need to be precise. Especially if it is sensitive data, like money.
Of course, all of these depend on your case, and there is no onesizefitsall solution. But keep in mind that Float has quite a few issues with it and shares them with Double. So, if you need to be more precise  use Decimal (even though it might not eliminate everything, it's better).
thanks for the good tip.
Great tip about number data types.
what about int? I store money in cents in int with a custom getter and setter that multiplies and devides by 100. But I am always not sure what i need to do, when I calculate taxes for example. Calculate in cents or in the getter value devided by 100
By the standard  you should do all of your calculations with an
int
as that's what will give you the most correct result.Calculating after a getter value practically removes the reason to have the cents in your database as it will still cause problems with floating points (0.01 + 0.02 = 0.03405 (random numbers))