Why Does PostgreSQL Integer Division Produce Unexpected Results, and How Can I Fix It?

Division Operation Inaccuracy in PostgreSQL

When performing division (/) operations in PostgreSQL, it is crucial to note that the result may not be as expected, especially when dealing with integer data types. In this case, the division truncates the result towards zero, which can lead to incorrect answers.

To illustrate the issue, consider a table named "software" with two integer columns: "dev_cost" and "sell_cost". If "dev_cost" is 16000 and "sell_cost" is 7500, dividing "dev_cost" by "sell_cost" using the following query:

select dev_cost / sell_cost from software ;

will return the result 2. However, the correct answer is 3, indicating that 3 units of software need to be sold to recover the development cost.

To resolve this issue, it is necessary to ensure that at least one of the values in the division operation is cast to a float or decimal data type. This allows for accurate floating-point calculations, preserving the fractional part of the result. One way to achieve this is by casting the "dev_cost" column to a decimal type in the query:

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

Alternatively, you can simplify the casting operation using the PostgreSQL type cast operator:

select dev_cost::decimal / sell_cost from software ;

Finally, to obtain an integer result rounded up to the nearest whole number, you can use the ceil() function within the query:

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

By following these guidelines, you can overcome the potential inaccuracies that arise from integer division in PostgreSQL and ensure accurate mathematical operations on your numerical data.

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