In mathematics, the absolute value (or modulus) | a | of a real number a is the non-negative value of a without regard to its sign. Namely, | a | = a for a positive a, | a | = −a for a negative a, and | 0 | = 0. For example, the absolute value of 3 is 3, and the absolute value of −3 is also 3. The absolute value of a number may be thought of as its distance from zero.
Generalizations of the absolute value for real numbers occur in a wide variety of mathematical settings. For example an absolute value is also defined for the complex numbers, the quaternions, ordered rings, fields and vector spaces. The absolute value is closely related to the notions of magnitude, distance, and norm in various mathematical and physical contexts.
When you want to have the absolute value from a number (or any other type that can be converted to a numeric type) you can use the abs SQL function in the Oracle database.
SELECT ABS(-20) "absovalue" FROM DUAL; absovalue ---------- 20