Why Does MySQL Struggle with Comparing Floating-Point Values?

MySQL's Pitfalls in Comparing Floating-Point Values

Floating-point calculations in MySQL can lead to erroneous comparisons due to inherent precision limitations. To address this issue, consider using theDECIMAL type instead.

Intrinsic Imprecision of Floating-Point Arithmetic

Floating-point numbers are stored with limited precision, which can introduce slight inaccuracies during calculations. For instance, consider the number 50.12 stored as a float in MySQL:

CREATE TABLE users (points FLOAT);
INSERT INTO users (points) VALUES (50.12);

When comparing this value with 12.75 using the operator >, MySQL returns "False," even though 50.12 is greater than 12.75.

SELECT COUNT(*) FROM users WHERE points > 12.75;

The DECIMAL Advantage

To avoid such inconsistencies, the DECIMAL data type provides fixed precision and scale, ensuring that calculations and comparisons are accurate. For example:

ALTER TABLE users MODIFY COLUMN points DECIMAL(6,2);
UPDATE users SET points = 50.12;
SELECT COUNT(*) FROM users WHERE points > 12.75;

Now, the comparison returns "True," as intended.

Additional Considerations

• Use the DEFAULT keyword to specify a default value for floating-point columns, avoiding NULL values.
• Consider using ROUND() or TRUNCATE() functions before performing comparisons to mitigate rounding errors.

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