Division ( / ) not giving my answer in postgresql

Question

I have a table software and columns in it as dev_cost, sell_cost. If dev_cost is 16000 and sell_cost is 7500.

How do I find the quantity of software to be sold in order to recover the dev_cost?

I have queried as below:

select dev_cost / sell_cost from software ;

It is returning 2 as the answer. But we need to get 3, right?

What would be the query for that? Thanks in advance.

Solution 1

Your columns have integer types, and integer division truncates the result towards zero. To get an accurate result, you'll need to cast at least one of the values to float or decimal:

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

or just:

select dev_cost::decimal / sell_cost from software ;

You can then round the result up to the nearest integer using the ceil() function:

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

(See demo on SQLFiddle.)

Solution 2

You can cast integer type to numeric and use ceil() function to get the desired output

The PostgreSQL ceil function returns the smallest integer value that is greater than or equal to a number.

SELECT 16000::NUMERIC / 7500 col 
      ,ceil(16000::NUMERIC / 7500) 

Result:

col                  ceil 
------------------   ---- 
2.1333333333333333     3    

So your query should be

select ceil(dev_cost::numeric/sell_cost) 
from software

Solution 3

You can also cast your variable to the desired type, then apply division:

 SELECT (dev_cost::numeric/sell_cost::numeric);

You can round your value , and specify the number of digits after point:

SELECT TRUNC((dev_cost::numeric/sell_cost::numeric),2);

Solution 4

This query will round result to next integer

select round(dev_cost ::decimal / sell_cost + 0.5)

View more solutions

Comments

[zeewagon]

If sell_cost is 7500, we need to sell 3 software to recover dev_cost i.e. > 16000. That is my question

[Vivek S.]

try select ceil(16000::numeric/7500)

[zeewagon]

select ceil(dev_cost::numeric/sell_cost) from software; --worked

[Mike Sherrill 'Cat Recall']

We're talking about money. Cast to decimal, not float.

[Ilmari Karonen]

@Mike: Good point, although unlikely to matter in the OP's case. (All they're asking for is integer division that rounds up; floats will do just fine as an intermediate type for that, at least unless the original values are bigints.) Still, fixed.

[Ilmari Karonen]

This will give the wrong result if dev_cost happens to be an integer multiple of sell_cost: see example.

[zeewagon]

This query is ok. But if the table more values, say for example, dev_cost is 6000 and sell_cost is 400, the answer 15 would be correct. But your query gives 16 as the answer. What should we do? I am new to SQL, correct me if I am wrong.

[Ilmari Karonen]

@MRah: Glad to be of assistance. :) BTW, instead of commenting on answers that you find useful, you can vote them up by clicking the upwards-pointing triangle icon in the top left corner of the answer. This will reward the answerer with reputation points and lets them know that their answer is appreciated, and it also helps the best answers rise to the top of the page.

[o.v]

Is there any real need to use ::decimal for each operand?

[J. B. Rainsberger]

Either round() or floor(x + 0.5), but not round(x + 0.5)