Equivalent Comparison Failures with Floating-Point Numbers

Possible Causes

Equivalent comparison of floating-point numbers is a common problem. In computing, floating-point numbers are stored as approximate values instead of exact values. Therefore, unexpected problems may occur during equivalent comparison and mathematical operations.

In RDS for MySQL, FLOAT and DOUBLE are floating-point types. The following figure shows an example for equivalent comparison using floating-point numbers:

Solution

1. Decide on an acceptable tolerance for differences between the field and the value and then do the comparison against the tolerance value. Example:

   

2. Use the fixed-point number type (DECIMAL) to replace the floating-point number type. Example: