Adding subqueries when one is null [duplicate] - mysql

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?

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.

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).

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.

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.

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;

Related

MySQL: Get total number of customers and total of each status within a store [duplicate]

I have two tables, one is for news and the other one is for comments and I want to get the count of the comments whose status has been set as approved.
SELECT
ccc_news . *,
count(if(ccc_news_comments.id = 'approved', ccc_news_comments.id, 0)) AS comments
FROM
ccc_news
LEFT JOIN
ccc_news_comments
ON ccc_news_comments.news_id = ccc_news.news_id
WHERE
`ccc_news`.`category` = 'news_layer2'
AND `ccc_news`.`status` = 'Active'
GROUP BY
ccc_news.news_id
ORDER BY
ccc_news.set_order ASC
LIMIT 20
But the problem with this query is that the minimum value that is fetched for the comments column is 1 whether there is any comment existent corresponding to that news or not.
Any help would be highly appreciable.
Use sum() in place of count()
Try below:
SELECT
ccc_news . * ,
SUM(if(ccc_news_comments.id = 'approved', 1, 0)) AS comments
FROM
ccc_news
LEFT JOIN
ccc_news_comments
ON
ccc_news_comments.news_id = ccc_news.news_id
WHERE
`ccc_news`.`category` = 'news_layer2'
AND `ccc_news`.`status` = 'Active'
GROUP BY
ccc_news.news_id
ORDER BY
ccc_news.set_order ASC
LIMIT 20
Better still (or shorter anyway):
SUM(ccc_news_comments.id = 'approved')
This works since the Boolean type in MySQL is represented as INT 0 and 1, just like in C. (May not be portable across DB systems though.)
As for COALESCE() as mentioned in other answers, many language APIs automatically convert NULL to '' when fetching the value. For example with PHP's mysqli interface it would be safe to run your query without COALESCE().
This should work:
count(if(ccc_news_comments.id = 'approved', ccc_news_comments.id, NULL))
count() only check if the value exists or not. 0 is equivalent to an existent value, so it counts one more, while NULL is like a non-existent value, so is not counted.
Replace this line:
count(if(ccc_news_comments.id = 'approved', ccc_news_comments.id, 0)) AS comments
With this one:
coalesce(sum(ccc_news_comments.id = 'approved'), 0) comments
count(ccc_news_comments.id = 'approved' or null)
More concise

SUM inside SUM SQL Invalid use of group function

Hi I want to perform a calculation inside a SUM with my sql, but there is one SUM field that consist of other SUM fields. I get the General error: 1111 Invalid use of group function. What is the proper way of summing other sum fields in SQL?
I can't use the alias of other sum fields to perform the calculation because it says that the alias is unidentified.
This part is my problem
SUM((SUM(transactions.payable) + SUM(transactions.discount) ) - SUM(deliveries.delivery_fee) ) AS raw_sales
Thank you
Here is my SQL.
SELECT
MONTHNAME(transactions.date_transac) AS MONTH,
SUM(transactions.payable) AS total,
SUM(transactions.discount) AS discount,
SUM(deliveries.delivery_fee) AS delivery,
SUM(
(
SUM(transactions.payable) + SUM(transactions.discount)
) - SUM(deliveries.delivery_fee)
) AS raw_sales,
MONTH(transactions.date_transac) AS monthnum
FROM
`transactions`
LEFT JOIN `requisitions` ON `transactions`.`requisition_id` = `requisitions`.`id`
LEFT JOIN `transactions` AS `ct`
ON
`transactions`.`code` = `ct`.`charge_transaction_code`
LEFT JOIN `deliveries` ON `transactions`.`delivery_id` = `deliveries`.`id`
WHERE
`transactions`.`transaction_type` = Sale AND YEAR(`transactions`.`date_transac`) = 2020
GROUP BY
`month`
ORDER BY
`monthnum` ASC
enter image description here
You can't nest aggregate functions. Here, I suspect that you could move the arithmetics within the aggregate function rather than attempting to nest:
SUM(
transactions.payable
+ transactions.discount
- COALESCE(deliveries.delivery_fee, 0)
) AS raw_sales
delivery_fee comes from a left join table so it could be null, hence we use coalesce().
That said, I am quite suspicious about the logic of your query. I am wondering, for example, why transactions appears twice in the from clause. There are also missing quotes around literal string "Sale" in the WHERE clause. If you were to ask a legitimate question, including sample data, desired results, and an explanation of the purpose of the query, one might be able to suggests optimizations.
The query just worked, I haven't realized that it is no longer necessary to calculate all Sum fields. I just removed the external sum.

SQL: Something wrong with inheriting variables for NULL next-row values

I'm trying to inherit value from previous row (based on correct subscription_id + checking for IS NULL subscription_status), but something goes wrong and I get incorrect value.
Take a look at screenshot.
If I'm not mistaken it also called last non-null puzzle, but examples of possible solution for other DB provide window function with IGNORE NULLS.
But, I'm using MySQL 8.x and it doesn't support this function.
I'm sorry, but SQL fiddle doesn't provide correct text-value for variables in my code :(
https://www.db-fiddle.com/f/wHanqoSCHKJHus5u6BU4DB/4
Or, you can see mistakes here:
SET #history_subscription_status = NULL;
SET #history_subscription_id = 0;
SELECT
c.date,
c.user_id,
c.subscription_id,
sd.subscription_status,
(#history_subscription_id := c.subscription_id) as 'historical_sub_id',
(#history_subscription_status := CASE
WHEN #history_subscription_id = c.subscription_id AND sd.subscription_status IS NULL
THEN #history_subscription_status
ELSE
sd.subscription_status
END
) as 'historical'
FROM
calendar c
LEFT JOIN
subscription_data sd ON sd.date = c.date AND sd.user_id = c.user_id AND sd.subscription_id = c.subscription_id
ORDER BY
c.user_id,
c.subscription_id,
c.date
I expect to get results for this query in this way:
IMPORTANT: I'm going to use this code for a lot of data (about 1 mln rows), so it very important for me to avoid additional select or subquery that can slow down the execution of the query.

mysql reference not supported to group function

I have a MySQL procedure that takes in 2 parameters par_DateFrom and par_DateTo
I'm getting a nasty error. I'm pretty sure that reusing alias TotalDaysOut to calculate TotalIncome is the culprit. How can I fix this elegantly?
Error 1247:
reference TotalDaysOutnot supported reference to group function
BEGIN
SELECT t.LicencePlate
,f.Make
,f.Model
,f.Year
,COUNT(t.LicencePlate) AS TotalTrx
,SUM(DATEDIFF(IF(checkedIn >par_DateTo, par_DateTo, checkedIn) ,IF(checkedOut <par_DateFrom, par_DateFrom, checkedOut))) AS TotalDaysOut
,SUM(t.Price* (SELECT TotalDaysOut)) AS TotalIncome
FROM TRANSACTIONS t
INNER JOIN FLEET f
ON t.LicencePlate = f.LicencePlate
WHERE t.CheckedOut < par_DateTo AND t.CheckedIn > par_DateFrom
GROUP BY t.LicencePlate
,f.Make
,f.Model
,f.Year;
END
Since your predicates are already verifying that all of the columns referenced in the expression are not null:
checkedIn
par_DateTo
checkedOut
par_DateFrom
(The predicates in the WHERE clause require all of those to be non-NULL), you could simplify the expression a bit, to reference each column once, rather than twice:
DATEDIFF(LEAST(t.checkedIn, par_DateTo),GREATEST(t.checkedOut, par_DateFrom))
And (as Gordon already suggested) just repeat that expression where the result is needed.
When we absolutely, positively have to have reference to an alias from a query, the only real option in MySQL is to use an inline view, though this approach has significant performance consequences for large sets.
SELECT v.LicencePlate
, f.Make
, f.Model
, f.Year
, COUNT(v.LicencePlate) AS TotalTrx
, SUM(v.DaysOut) AS TotalDaysOut
, SUM(v.DaysOut)*v.Price AS TotalIncome
FROM ( SELECT t.LicencePlate
, t.Price
, DATEDIFF(
LEAST(t.checkedIn, par_DateTo),
GREATEST(t.checkedOut, par_DateFrom)
) AS DaysOut
FROM TRANSACTIONS t
WHERE t.CheckedOut < par_DateTo
AND t.CheckedIn > par_DateFrom
) v
JOIN FLEET f
ON f.LicencePlate = v.LicencePlate
GROUP
BY v.LicencePlate
, f.Make
, f.Model
, f.Year
That's less performant, and less elegant, than just simplifying and repeating the expression.
You can't do that. You cannot reference a column alias at the same level of the select as where it is defined. I'm not sure what the exact error is but the (select TotalDaysOut) doesn't make sense.
So, repeat the expression with the additional multiplication:
SUM(DATEDIFF(IF(checkedIn >par_DateTo, par_DateTo, checkedIn) ,IF(checkedOut <par_DateFrom, par_DateFrom, checkedOut))) AS TotalDaysOut,
SUM(t.Price * DATEDIFF(IF(checkedIn >par_DateTo, par_DateTo, checkedIn) ,IF(checkedOut <par_DateFrom, par_DateFrom, checkedOut))) AS TotalIncome

MySQL row subquery (multiple columns) with CASE (not in where-clause)

I want to retrieve two columns from the same table, but only if a certain column in the current row isn't set. With just one column to retrieve, there is no problem. Once I need another column, it appears that I need another subquery with another case-clause, but that seems really ineffective. I've never used Joins before, but I'm thinking it's probably really complicated with the case clause?!
I thought the beauty of it was that it actually only executed the (as I heard) wasteful subquery in the few cases when it's needed.
In the docs, I found that comparisons using ROW() are apparently possible. Is there an equivalent for retrieving the columns with AS?
Thank you for any hints, if it only works with Joins, please give me a push in the right direction since they seem kind of complicated and with the case clause it's probably gonna be a mess if I just go ahead.
Ruben
SELECT id, bekannt, (
CASE WHEN bekannt = ''
THEN (
SELECT bekannt
FROM vokabeln AS v2
WHERE v2.id = vokabeln.hinweis
LIMIT 1
)
ELSE NULL
END
) AS lueckentext, (
CASE WHEN bekannt = ''
THEN (
SELECT hinweis
FROM vokabeln AS v2
WHERE v2.id = vokabeln.hinweis
LIMIT 1
)
ELSE NULL
END
) AS lthinweis
FROM vokabeln
WHERE nutzer = 'test'
I'd code it as:
SELECT
v1.id, v1.bekannt, v2.bekannt AS lueckentext, v2.hinweis AS lthinweis
FROM
vokabeln AS v1
LEFT OUTER JOIN vokabeln AS v2
ON (v1.bekannt='' AND v2.id = v1.hinweis)
WHERE
v1.nutzer='test'