Mysql return 0 not null in sum - mysql

Question

Help needed please I have a table with taskId, Materials, Labour and a table with expenses in. The issue i have is that some tasks do not have and expense column in the taskenpense table so the column returns null. I need null to be 0.
` CREATE TABLE emptasks ( empTaskId INT, taskMaterials NUMERIC(8,2),taskLabour NUMERIC(8,2));
INSERT INTO emptasks VALUES
(1, 50, 50),
(2, 450.26, 50),
(3, 2505.10, 50),
(4, 2505.10, 50),
(5, 500, 500),
(6, 1000, 50);
CREATE TABLE taskexpenses (
feeID INT,
empTaskId INT,
expense NUMERIC(8,2));
INSERT INTO taskexpenses VALUES
(1, 1, 50.00),
(1, 2, 50.00),
(2, 2, 126.00),
(3, 3, 50.00),
(4, 4, 50.00),
(2, 2, 1206.00);
SELECT
p.empTaskId,
p.Labour,
p.Materials,
f.Expenses,
p.Labour + p.Materials - f.Expenses AS Total,
ROUND( (f.Expenses + p.Materials) / p.Labour * 100, 2) AS Percentage
FROM (
SELECT
empTaskId,
SUM(taskMaterials) AS Labour,
SUM(taskLabour) AS Materials
FROM emptasks
GROUP BY empTaskId
) p
LEFT JOIN (
SELECT taskexpenses.empTaskId,
SUM(expense) AS Expenses
FROM emptasks
INNER JOIN taskexpenses ON emptasks.empTaskId = taskexpenses.empTaskId
GROUP BY empTaskId
) f ON p.empTaskId = f.empTaskId
the result is
empTaskId Labour Materials Expenses Total Percentage
1 50 50 50 50 200
2 450.26 50 1382 -881.74 318.04
3 2505.1 50 50 2505.1 3.99
4 2505.1 50 50 2505.1 3.99
5 500 500 (null) (null) (null)
6 1000 50 (null) (null) (null)
I need the null value to return 0 so the sum can be worked out
FIDDLE LINK
THanks
Jon

Answer 1

Slightly simpler than in the answer from #Bob Jarvis is to use the IFNULL() function.
SELECT
p.empTaskId,
p.Labour,
p.Materials,
IFNULL(f.Expenses, '0') AS Expenses,
IFNULL(p.Labour + p.Materials - f.Expenses, '0') AS Total,
IFNULL(ROUND( (f.Expenses + p.Materials) / p.Labour * 100, 2), '0') AS Percentage
FROM ...
See fiddle

Answer 2

Use the COALESCE function:
SELECT p.empTaskId,
p.Labour,
p.Materials,
COALESCE(f.Expenses, 0) AS Expenses,
COALESCE(p.Labour, 0) + COALESCE(p.Materials, 0) - COALESCE(f.Expenses, 0) AS Total,
ROUND( (COALESCE(f.Expenses, 0) + COALESCE(p.Materials, 0)) / p.Labour * 100, 2) AS Percentage
FROM (SELECT empTaskId,
SUM(COALESCE(taskMaterials, 0)) AS Labour,
SUM(COALESCE(taskLabour, 0)) AS Materials
FROM emptasks
GROUP BY empTaskId) p
LEFT JOIN (SELECT taskexpenses.empTaskId,
SUM(COALESCE(expense, 0)) AS Expenses
FROM emptasks
INNER JOIN taskexpenses
ON emptasks.empTaskId = taskexpenses.empTaskId
GROUP BY empTaskId) f
ON p.empTaskId = f.empTaskId
Note that here I've put COALESCE on just about everything which might possibly be NULL. If you only want to put it on the Expenses column change it to be what you want.
Best of luck.