How Does PostgreSQL Handle Integer Division, and How Can I Get Accurate Results?

Division Operator in PostgreSQL: Understanding Integer Truncation and Floating-Point Calculations

In PostgreSQL, division operations (/) can lead to unexpected results when working with integer values. Understanding the underlying behavior of integer division is crucial to avoid incorrect calculations.

Consider the following query:

SELECT dev_cost / sell_cost FROM software

Where dev_cost is 16000 and sell_cost is 7500. You might expect the result to be 3, but it returns 2. This is because integer division truncates any fractional part of the result.

To obtain the desired value, you need to cast at least one of the values to a floating-point type (e.g., decimal) or use the :: operator to convert it on the fly:

SELECT CAST(dev_cost AS DECIMAL) / sell_cost FROM software

SELECT dev_cost::DECIMAL / sell_cost FROM software

These queries will return 2.133, which is the actual division result.

Additionally, you can use the ceil() function to round the result up to the nearest integer:

SELECT CEIL(dev_cost::DECIMAL / sell_cost) FROM software

This query will return 3, which is the desired quantity of software to recover the development cost.

It's important to be aware of this behavior when performing division operations and to use appropriate data types and casting to ensure accurate calculations.

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