php query floating point field

In PHP, you may encounter some problems when querying floating-point fields. This article explains how to resolve these issues to ensure accurate querying of floating point fields.

1. Understanding floating point types

Before we start solving the problem, we need to understand some knowledge about floating point types. Floating point data represents some decimal and/or exponent. Inside the computer, they are represented in scientific notation: a * 10^n. Among them, a is the decimal part of the number and n is the exponent part. Floating-point data are very precise, but precision issues sometimes arise because computers need to round when representing them.

2. The root of the problem

When querying floating-point fields, the main reason for the problem is PHP's rounding when expressing floating-point fields. Since computers use binary internally and floating-point data usually uses decimal, rounding errors sometimes occur when converting decimal floating-point to binary. This leads to precision errors that may occur when querying floating-point fields in PHP.

3. Solution

In order to ensure the accuracy of querying floating-point fields, we can use the following two solutions:

3.1 String comparison

This method ensures that floating point data uses completely accurate values ​​when comparing. String comparisons treat floating point numbers as strings rather than understanding their numeric values. This works in most cases, but it can cause efficiency issues if you need to do a lot of comparisons.

For example, suppose we have a floating-point field price, whose value is 8.6. We can set the query string to:

SELECT * FROM products WHERE price = '8.6';

This will ensure that the query uses completely exact values ​​for comparison.

3.2 Error range comparison

In this method, we will compare floating point numbers with an error range instead of directly comparing their exact values. This allows us to handle small fluctuations caused by rounding errors and compare the precision of floating point numbers. This can be achieved in the following way:

SELECT * FROM products WHERE price BETWEEN 8.5 AND 8.7;

This query will return all price values ​​between 8.5 and 8.7 (including these two values) product.

4. Summary

In PHP, each floating point type has a different sign bit, exponent bit and mantissa bit, which means that different types of floating point Points may be rounded differently. To ensure the accuracy of querying floating point fields, we can use string comparison or error range comparison. String comparison uses fully exact values ​​for comparison, while error range comparison allows us to compare floating point numbers with a certain error.

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