Is converting product price to cents the best way to store value in the database?

[imgrooot]

Say I have two functions that convert from Dollar to Cents and Cents to Dollar.

function convertToDollar($value) {
    $amount = $value / 100;
    return $amount;
}

function convertToCents($value) {
    $amount = $value * 100;
    return $amount;
}

Currently I convert all the Dollar amounts to cents and store the cents in the mysql database column. When I showcase those amounts on a page, I simply convert the Cents back to Dollar.

Am I doing this correctly or is there a better way to store product pricing in mysql table?

[Barand]

I store prices as decimal EG

+-------------+------------------+------+-----+----------------------+--------------------------------+
| Field       | Type             | Null | Key | Default              | Extra                          |
+-------------+------------------+------+-----+----------------------+--------------------------------+
| prod_id     | int(11)          | NO   | PRI | NULL                 | auto_increment                 |
| description | varchar(50)      | YES  |     | NULL                 |                                |
| price       | decimal(10,2)    | YES  |     | NULL                 |                                |
+-------------+------------------+------+-----+----------------------+--------------------------------+

 

Query example...

TABLE: product                                     TABLE: cart
+---------+-------------+--------+                 +----+---------+------+
| prod_id | description | price  |                 | id | prod_id | qty  |
+---------+-------------+--------+                 +----+---------+------+
|       1 | Product AZ  |  49.99 |                 |  1 |       1 |    2 |
|       2 | Product B   |  29.99 |                 |  2 |       3 |    5 |
|       3 | Product C   |   9.99 |                 |  3 |       7 |    1 |
|       4 | Product D   |  22.99 |                 |  4 |       6 |    2 |
|       5 | Product E   |  29.99 |                 +----+---------+------+
|       6 | Product F   |  19.99 |
|       7 | Product G   | 129.99 |
|       8 | Product H   |  99.99 |
|       9 | Product I   |  74.99 |
|      10 | Product J   |  69.99 |
+---------+-------------+--------+

SELECT p.prod_id
     , p.description
     , p.price
     , c.qty
     , p.price * c.qty as total
FROM test_product p
         JOIN
     test_cart c USING (prod_id);
     
+---------+-------------+--------+------+--------+
| prod_id | description | price  | qty  | total  |
+---------+-------------+--------+------+--------+
|       1 | Product AZ  |  49.99 |    2 |  99.98 |
|       3 | Product C   |   9.99 |    5 |  49.95 |
|       7 | Product G   | 129.99 |    1 | 129.99 |
|       6 | Product F   |  19.99 |    2 |  39.98 |
+---------+-------------+--------+------+--------+

 

[requinix]

To explain, the thing about converting to cents is because integers are precise while floating-point numbers (non-integers) are not precise. And when it comes to currency, being precise is very important.
What DECIMAL does is give you something that looks like a non-integer, except it's precise. In exchange for the precision, you have to tell the database exactly how precise you want and you won't be able to store anything smaller. But that's perfectly fine for you because you don't care about anything more than two decimal places for cents.

[imgrooot]

49 minutes ago, Barand said:

I store prices as decimal EG

+-------------+------------------+------+-----+----------------------+--------------------------------+
| Field       | Type             | Null | Key | Default              | Extra                          |
+-------------+------------------+------+-----+----------------------+--------------------------------+
| prod_id     | int(11)          | NO   | PRI | NULL                 | auto_increment                 |
| description | varchar(50)      | YES  |     | NULL                 |                                |
| price       | decimal(10,2)    | YES  |     | NULL                 |                                |
+-------------+------------------+------+-----+----------------------+--------------------------------+

 

Query example...

TABLE: product                                     TABLE: cart
+---------+-------------+--------+                 +----+---------+------+
| prod_id | description | price  |                 | id | prod_id | qty  |
+---------+-------------+--------+                 +----+---------+------+
|       1 | Product AZ  |  49.99 |                 |  1 |       1 |    2 |
|       2 | Product B   |  29.99 |                 |  2 |       3 |    5 |
|       3 | Product C   |   9.99 |                 |  3 |       7 |    1 |
|       4 | Product D   |  22.99 |                 |  4 |       6 |    2 |
|       5 | Product E   |  29.99 |                 +----+---------+------+
|       6 | Product F   |  19.99 |
|       7 | Product G   | 129.99 |
|       8 | Product H   |  99.99 |
|       9 | Product I   |  74.99 |
|      10 | Product J   |  69.99 |
+---------+-------------+--------+

SELECT p.prod_id
     , p.description
     , p.price
     , c.qty
     , p.price * c.qty as total
FROM test_product p
         JOIN
     test_cart c USING (prod_id);
     
+---------+-------------+--------+------+--------+
| prod_id | description | price  | qty  | total  |
+---------+-------------+--------+------+--------+
|       1 | Product AZ  |  49.99 |    2 |  99.98 |
|       3 | Product C   |   9.99 |    5 |  49.95 |
|       7 | Product G   | 129.99 |    1 | 129.99 |
|       6 | Product F   |  19.99 |    2 |  39.98 |
+---------+-------------+--------+------+--------+

 

Wow that's a wonderful example.

I just have one question. Why use (10,2) instead of say (12,2)? Wouldn't it be safer to use a higher threshold if you're expecting bigger to store bigger numbers? 

[Barand]

If you are selling warships, why not indeed. Whatever your application requires. 

[imgrooot]

5 hours ago, Barand said:

If you are selling warships, why not indeed. Whatever your application requires. 

 

Ah good to know lol.

[Barand]

Plus I doubt if you'd be interested in the odd cents if you are selling a $5,000,000,000 aircraft carrier.

Although if your prices were in guineas...