Merging multiple MySQL SELECT statements calculating fields - mysql

Question

I've had a look at this question (Please help merging 4 MySQL queries to One) hoping it would help, but it doesn't. I can't make sense of it because my brain is fried.
I'm trying to get my head around merging four SELECT statements, all of which work individually, into one.
The fields are;
QUANTITY: INT;
ORDERDATE: DATE; // Not datetime - I don't need time.
MySQL Version 5.6.17
The data I'm retrieving is;
1) Number of products ordered this financial year;
SELECT SUM(QUANTITY) AS YTD
FROM ORDERDETAILS
WHERE ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16"
Note that in Australia the Financial Year is 1st of July through to 30th of June.
2) Number of products ordered this month;
SELECT SUM(QUANTITY) AS MONTHY
FROM ORDERDETAILS
WHERE ORDERDATE BETWEEN "2017-02-01" AND "2017-02-16"
3) Number of products ordered today;
SELECT SUM(QUANTITY) AS TODAYS
FROM ORDERDETAILS
WHERE ORDERDATE = "2017-02-16"
4) Average number of products ordered per order;
SELECT AVG(QUANTITY) AS BOOGER
FROM ORDERDETAILS
WHERE ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16"
I want to avoid sending four separate statements to the server. Perhaps it can't be done, but if I could achieve the same results in a single statement I'd be happy.
I've looked at joins, embedding select within selects but can't get my head around it.
Once I get the data all I do is update a couple of labels on a form (Delphi).
Any tips that a nearly 55 year old brain can handle would be appreciated.

Answer 1

You can do this using case when condition:
select
sum(case when ORDERDATE BETWEEN '2016-07-01' AND '2017-02-16' then QUANTITY end ) as YTD,
sum(case when ORDERDATE BETWEEN '2017-02-01' AND '2017-02-16' then QUANTITY end ) as MONTHY,
sum(case when ORDERDATE = '2017-02-16' then QUANTITY end ) as TODAYS,
AVG(case when ORDERDATE BETWEEN '2016-07-01' AND '2017-02-16' then QUANTITY end ) as BOOGER
FROM ORDERDETAILS

Answer 2

You simply have to use a different alias on the different calls to the table and put it all in one SELECT statement as follows:
SELECT SUM(od1.QUANTITY) AS YTD,
SUM(od2.QUANTITY) AS MONTHLY,
SUM(od3.QUANTITY) AS TODAYS,
AVG(od4.QUANTITY) AS BOOGER
FROM ORDERDETAILS od1,
ORDERDETAILS od2,
ORDERDETAILS od3,
ORDERDETAILS od4
WHERE od1.ORDERDATE BETWEEN CAST('2016-07-01' AS DATE) AND CAST('2017-02-16' AS DATE)
AND od2.ORDERDATE BETWEEN CAST('2017-02-01' AS DATE) AND CAST('2017-02-16' AS DATE)
AND od3.ORDERDATE = CAST('2017-02-16' AS DATE)
AND od4.ORDERDATE BETWEEN CAST('2016-07-01' AS DATE) AND CAST('2017-02-16' AS DATE)

Answer 3

Use SUM(IF()) pattern and move condition inside the IF.
SELECT
SUM(IF(ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16", QUANTITY, 0)) AS YTD,
SUM(IF(ORDERDATE BETWEEN "2017-02-01" AND "2017-02-16", QUANTITY, 0)) AS MONTHY,
SUM(IF(ORDERDATE = "2017-02-16", QUANTITY, 0)) AS TODAYS,
SUM(IF(ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16", QUANTITY, 0)) / COUNT(IF(ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16", 1, NULL)) AS BOOGER
FROM ORDERDETAILS
WHERE ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16";
Consider using CURDATE() for today's date.
Also a WHERE clause can be added so that all rows of table are not scanned e.g. WHERE ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16" after FROM ORDERDETAILS