Bug #101702 Submitted: Calculations based on backreference to subquery results in NULL 20 Nov 2020 16:58 20 Nov 2020 18:25 Billy Sullivan Can't repeat None MySQL Server: DML S3 (Non-critical) 8.0.21 Ubuntu Any

[20 Nov 2020 16:58] Billy Sullivan
Description:
Using referenced results from a subquery in a mathematical calculation sometimes results in a NULL value.

How to repeat:
DROP TABLE IF EXISTS `customer_transaction`;
CREATE TABLE `customer_transaction` (
`customer_transaction_id` int NOT NULL AUTO_INCREMENT,
`customer_id` int NOT NULL,
`order_id` int NOT NULL,
`amount` decimal(12,2) NOT NULL,
`credit_order_id` int NOT NULL,
`refund` int NOT NULL,
PRIMARY KEY (`customer_transaction_id`),
KEY `customer_id` (`customer_id`),
KEY `order_id` (`order_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

INSERT INTO `customer_transaction` VALUES (1,200,1000,200.00,500,1),(2,200,2000,-200.00,0,0),(3,200,0,0.00,0,2833);

SELECT credit_order_id,
(
SELECT IFNULL(SUM(amount),0) AS total_refunds
FROM customer_transaction ctr
WHERE ctr.credit_order_id = ct.credit_order_id
) AS refunds_issued,
SUM(ct.amount) AS total_amount,
SUM(ct.amount) - (SELECT refunds_issued)  AS refundable,
SUM(ct.amount) - (
SELECT IFNULL(SUM(amount),0) AS total_refunds
FROM customer_transaction ctr
WHERE ctr.credit_order_id = ct.credit_order_id
) AS refundable_2
FROM customer_transaction ct
WHERE ct.credit_order_id > 0
AND ct.amount > 0
GROUP BY credit_order_id;

The value `refundable` should be the same as `refundable_2` however it results in NULL on my version.  Note: I was unable to reproduce this on any DB Fiddle using a different version so it's possibly fixed in 8.0.22.
[20 Nov 2020 18:18] MySQL Verification Team
Thank you for the bug report. I couldn't repeat with 8.0.22:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 16
Server version: 8.0.22 MySQL Community Server - GPL

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> USE test
Database changed
mysql> DROP TABLE IF EXISTS `customer_transaction`;
Query OK, 0 rows affected, 1 warning (0.05 sec)

mysql> CREATE TABLE `customer_transaction` (
->   `customer_transaction_id` int NOT NULL AUTO_INCREMENT,
->   `customer_id` int NOT NULL,
->   `order_id` int NOT NULL,
->   `amount` decimal(12,2) NOT NULL,
->   `credit_order_id` int NOT NULL,
->   `refund` int NOT NULL,
->   PRIMARY KEY (`customer_transaction_id`),
->   KEY `customer_id` (`customer_id`),
->   KEY `order_id` (`order_id`)
-> ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
Query OK, 0 rows affected, 1 warning (0.11 sec)

mysql>
mysql> INSERT INTO `customer_transaction` VALUES (1,200,1000,200.00,500,1),(2,200,2000,-200.00,0,0),(3,200,0,0.00,0,2833);
Query OK, 3 rows affected (0.02 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql>
mysql> SELECT credit_order_id,
->     (
->         SELECT IFNULL(SUM(amount),0) AS total_refunds
->         FROM customer_transaction ctr
->         WHERE ctr.credit_order_id = ct.credit_order_id
->     ) AS refunds_issued,
->     SUM(ct.amount) AS total_amount,
->     SUM(ct.amount) - (SELECT refunds_issued)  AS refundable,
->     SUM(ct.amount) - (
->         SELECT IFNULL(SUM(amount),0) AS total_refunds
->         FROM customer_transaction ctr
->         WHERE ctr.credit_order_id = ct.credit_order_id
->     ) AS refundable_2
-> FROM customer_transaction ct
-> WHERE ct.credit_order_id > 0
->     AND ct.amount > 0
-> GROUP BY credit_order_id;
+-----------------+----------------+--------------+------------+--------------+
| credit_order_id | refunds_issued | total_amount | refundable | refundable_2 |
+-----------------+----------------+--------------+------------+--------------+
|             500 |         200.00 |       200.00 |       0.00 |         0.00 |
+-----------------+----------------+--------------+------------+--------------+
1 row in set (0.06 sec)

mysql>

================================================================================
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.21 MySQL Community Server - GPL

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> CREATE DATABASE test
-> ;
Query OK, 1 row affected (0.01 sec)

mysql> USE test
Database changed
mysql> DROP TABLE IF EXISTS `customer_transaction`;
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql> CREATE TABLE `customer_transaction` (
->   `customer_transaction_id` int NOT NULL AUTO_INCREMENT,
->   `customer_id` int NOT NULL,
->   `order_id` int NOT NULL,
->   `amount` decimal(12,2) NOT NULL,
->   `credit_order_id` int NOT NULL,
->   `refund` int NOT NULL,
->   PRIMARY KEY (`customer_transaction_id`),
->   KEY `customer_id` (`customer_id`),
->   KEY `order_id` (`order_id`)
-> ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
Query OK, 0 rows affected, 1 warning (0.03 sec)

mysql>
mysql> INSERT INTO `customer_transaction` VALUES (1,200,1000,200.00,500,1),(2,200,2000,-200.00,0,0),(3,200,0,0.00,0,2833);
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql>
mysql> SELECT credit_order_id,
->     (
->         SELECT IFNULL(SUM(amount),0) AS total_refunds
->         FROM customer_transaction ctr
->         WHERE ctr.credit_order_id = ct.credit_order_id
->     ) AS refunds_issued,
->     SUM(ct.amount) AS total_amount,
->     SUM(ct.amount) - (SELECT refunds_issued)  AS refundable,
->     SUM(ct.amount) - (
->         SELECT IFNULL(SUM(amount),0) AS total_refunds
->         FROM customer_transaction ctr
->         WHERE ctr.credit_order_id = ct.credit_order_id
->     ) AS refundable_2
-> FROM customer_transaction ct
-> WHERE ct.credit_order_id > 0
->     AND ct.amount > 0
-> GROUP BY credit_order_id;
+-----------------+----------------+--------------+------------+--------------+
| credit_order_id | refunds_issued | total_amount | refundable | refundable_2 |
+-----------------+----------------+--------------+------------+--------------+
|             500 |         200.00 |       200.00 |       NULL |         0.00 |
+-----------------+----------------+--------------+------------+--------------+
1 row in set (0.00 sec)
[20 Nov 2020 18:25] Billy Sullivan
Thanks, I guess it's fixed! Now just have to wait for the new version to make it into our repo.

By any chance can I get a reference for the change that addresses this?