Syntax
------ 
-
 
Description
----------- 
Subtraction. The operator is also used as the unary minus
for changing sign.
 
If both operands are integers, the result is calculated with
BIGINT precision. If either integer is unsigned, the result
is also an unsigned integer, unless the
NO_UNSIGNED_SUBTRACTION SQL_MODE is enabled, in which case
the result is always signed.
 
For real or string operands, the operand with the highest
precision determines the result precision.
 
Examples
-------- 
SELECT 96-9;
 
+------+
| 96-9 |
+------+
| 87 |
+------+
 
SELECT 15-17;
 
+-------+
| 15-17 |
+-------+
| -2 |
+-------+
 
SELECT 3.66 + 1.333;
 
+--------------+
| 3.66 + 1.333 |
+--------------+
| 4.993 |
+--------------+
 
Unary minus:
 
 SELECT - (3+5);
+---------+
| - (3+5) |
+---------+
| -8 |
+---------+
 


URL: https://mariadb.com/kb/en/subtraction-operator-/