How Can I Correctly Calculate the Result of Integer Division in PostgreSQL to Avoid Truncation?

Division ( / ) Miscalculating in PostgreSQL

You're encountering a division issue in PostgreSQL where integer division results in an inaccurate answer. Let's delve into the background and provide a solution that addresses the problem.

Understanding Integer Division

Integer division, denoted by "/", truncates the quotient towards zero. This means that when dividing two integers, the result is rounded down to the nearest whole number.

In the given example, "dev_cost" and "sell_cost" are both integers. Therefore, the query "select dev_cost / sell_cost" returns 2, which is the integer equivalent of 16000 divided by 7500. However, you require the quantity of software to recover the dev_cost, which is 3.

Solving the Calculation Issue

To obtain the precise value, we need to ensure that at least one operand in the division is a floating-point or decimal value. This prevents the truncation and results in a fractional quotient.

One solution is to cast one of the columns to decimal using the "CAST" operator:

select cast(dev_cost as decimal) / sell_cost from software ;

Another alternative is to use the "::decimal" syntax to cast the dev_cost column:

select dev_cost::decimal / sell_cost from software ;

Both of these approaches will return a floating-point result, representing the exact quantity of software required.

Rounding Up to the Nearest Integer

If you want to round the result to the nearest integer, representing the minimum quantity of software to recover the dev_cost, you can use the "CEIL" function:

select ceil(dev_cost::decimal / sell_cost) from software ;

This will round the decimal result up to the next whole number, ensuring that enough software is sold to cover the development cost.

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