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4. First, a quick review
So you think you can count?
Rounding functions and more
Review and practice


Before we continue, let's review what we already know about numbers. Integers are expressed in the following way: 1, 2, 43, -27, etc. Fractions are expressed with a dot (.): 12.45, -401.238, etc. Please note that in some languages, you use a comma instead of a dot, but not in SQL! For example, 12,45 is incorrect.

In PostgreSQL (and in most programming languages) there are three kinds of numbers:

  • Integer (integer): stores integers (e.g., -5, 0, 5, 42).
  • Floating-point (real, double precision): stores fractions by approximating them in binary.
  • Decimal (numeric): stores fractions in decimal format.

In this part, we'll discuss some of the differences between PostgreSQL's number data types.

Of course, you can use the four basic mathematical operations (add +, subtract -, multiply *, and divide /) with actual numbers in PostgreSQL. You can also use columns and constant numbers together. Take a look at the example below:

SELECT hp / 4 AS quarter_hp
FROM character;


For each character, display its name, level, and the sum of its hp and mp as the hmp column.

Stuck? Here's a hint!

You can add values of two columns with a plus (+).