SELECT records using multiple critira - mysql

Question

I have a table named all_data with fields date, value, and other fields.
I need to select last 7, 14, and 30 days from the database. There can be several entries with the same date like
date value
10-25-16 30
10-25-16 24
10-26-16 42
Here is the SELECT Statment I have that works for less than 30 days
$sql = "SELECT type_entry, COUNT(value) as val_count, FLOOR(SUM(value)) as sum_glu FROM all_data
WHERE DATEDIFF(NOW(), date) < 30 AND type_entry = 'Glucose'
ORDER BY date";
I want the same query 2 more times but changing the DATEDIFF statement with <14 and <7 so I end up with val_count1, val_count2, val_count3, sum_glu1, sum_glu2, sumglu3 I will use those to calculate the average of each.
I do not know enough SQL to figure out how to do it.
Here is a sample of readings
10/17/2016 116
10/17/2016 277
10/17/2016 145
10/18/2016 150
10/18/2016 125
10/19/2016 200
I need the number of records from 10/19/2016 for 7 days then I can do a weekly average of the readings.

Answer 1

You can use conditional aggregation here:
SELECT type_entry,
SUM(CASE WHEN DATEDIFF(NOW(), date) < 30 THEN 1 ELSE 0 END) AS val_count_30,
FLOOR(SUM(CASE WHEN DATEDIFF(NOW(), date) < 30 THEN value ELSE 0 END)) AS sum_glu_30,
SUM(CASE WHEN DATEDIFF(NOW(), date) < 14 THEN 1 ELSE 0 END) AS val_count_14,
FLOOR(SUM(CASE WHEN DATEDIFF(NOW(), date) < 14 THEN value ELSE 0 END)) AS sum_glu_14,
SUM(CASE WHEN DATEDIFF(NOW(), date) < 7 THEN 1 ELSE 0 END) AS val_count_7,
FLOOR(SUM(CASE WHEN DATEDIFF(NOW(), date) < 7 THEN value ELSE 0 END)) AS sum_glu_7
FROM all_data
WHERE type_entry = 'Glucose'
ORDER BY date
If you just want the average of value for a 7 day period starting on 10/19/2016 for 7 days then you can just use a WHERE clause:
SELECT type_entry,
AVG(value) AS avgValue
FROM all_data
WHERE date BETWEEN '2016-10-19' AND DATE_ADD('2016-10-19', INTERVAL 7 DAY) AND
type_entry = 'Glucose'
GROUP BY type_entry

Answer 2

Basically you can retrieve all rows with criteria < 30 and all your following criterias contain within this one. You could add a CASE expression within aggregate functions to only perform aggregation within rows that match your criteria. All I did was changed the < X for every pair of columns:
SELECT
type_entry,
COUNT(CASE WHEN DATEDIFF(NOW(), date) < 30 THEN value END) as val_count1,
FLOOR(SUM(CASE WHEN DATEDIFF(NOW(), date) < 30 THEN value END)) as sum_glu1,
COUNT(CASE WHEN DATEDIFF(NOW(), date) < 14 THEN value END) as val_count2,
FLOOR(SUM(CASE WHEN DATEDIFF(NOW(), date) < 14 THEN value END)) as sum_glu2,
COUNT(CASE WHEN DATEDIFF(NOW(), date) < 7 THEN value END) as val_count3,
FLOOR(SUM(CASE WHEN DATEDIFF(NOW(), date) < 7 THEN value END)) as sum_glu3
FROM all_data
WHERE DATEDIFF(NOW(), date) < 30 AND type_entry = 'Glucose'
GROUP BY type_entry
ORDER BY date
Also, note that I added the missing GROUP BY clause. Even though MySQL allows it, many different databases would yield an error. The recommended way is not to rely on MySQL mechanism in this matter.