Return 0 if field is null in MySQL - sql

Question

In MySQL, is there a way to set the "total" fields to zero if they are NULL?
Here is what I have:
SELECT uo.order_id, uo.order_total, uo.order_status,
(SELECT SUM(uop.price * uop.qty)
FROM uc_order_products uop
WHERE uo.order_id = uop.order_id
) AS products_subtotal,
(SELECT SUM(upr.amount)
FROM uc_payment_receipts upr
WHERE uo.order_id = upr.order_id
) AS payment_received,
(SELECT SUM(uoli.amount)
FROM uc_order_line_items uoli
WHERE uo.order_id = uoli.order_id
) AS line_item_subtotal
FROM uc_orders uo
WHERE uo.order_status NOT IN ("future", "canceled")
AND uo.uid = 4172;
The data comes out fine, except the NULL fields should be 0.
How can I return 0 for NULL in MySQL?

Answer 1

Use IFNULL:
IFNULL(expr1, 0)
From the documentation:
If expr1 is not NULL, IFNULL() returns expr1; otherwise it returns expr2. IFNULL() returns a numeric or string value, depending on the context in which it is used.

Answer 2

You can use coalesce(column_name,0) instead of just column_name. The coalesce function returns the first non-NULL value in the list.
I should mention that per-row functions like this are usually problematic for scalability. If you think your database may get to be a decent size, it's often better to use extra columns and triggers to move the cost from the select to the insert/update.
This amortises the cost assuming your database is read more often than written (and most of them are).

Answer 3

None of the above answers were complete for me.
If your field is named field, so the selector should be the following one:
IFNULL(`field`,0) AS field
For example in a SELECT query:
SELECT IFNULL(`field`,0) AS field, `otherfield` FROM `mytable`
Hope this can help someone to not waste time.

Answer 4

You can try something like this
IFNULL(NULLIF(X, '' ), 0)
Attribute X is assumed to be empty if it is an empty String, so after that you can declare as a zero instead of last value. In another case, it would remain its original value.
Anyway, just to give another way to do that.

Answer 5

Yes IFNULL function will be working to achieve your desired result.
SELECT uo.order_id, uo.order_total, uo.order_status,
(SELECT IFNULL(SUM(uop.price * uop.qty),0)
FROM uc_order_products uop
WHERE uo.order_id = uop.order_id
) AS products_subtotal,
(SELECT IFNULL(SUM(upr.amount),0)
FROM uc_payment_receipts upr
WHERE uo.order_id = upr.order_id
) AS payment_received,
(SELECT IFNULL(SUM(uoli.amount),0)
FROM uc_order_line_items uoli
WHERE uo.order_id = uoli.order_id
) AS line_item_subtotal
FROM uc_orders uo
WHERE uo.order_status NOT IN ("future", "canceled")
AND uo.uid = 4172;