sum-as-decimal.md

https://dev.mysql.com/doc/refman/8.0/en/group-by-functions.html#function_sum

const QST = 0.0975;
const GST = 0.05;
console.log(QST + GST);

Were you expecting 0.1475?

The result is 0.14750000000000002.

This is an example of double behaving in unintuitive ways.

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Using SUM() on double/float values can give you the above result, too. The solution is to convert the values to a DECIMAL(M, D) type, sum that, then convert the result back to a double.

The sumAsDecimal() function does this.