mysql LEFT JOIN followed by GROUP BY with BETWEEN Ranges - mysql

Question

I am stumped with how I should proceed. Here is my current LEFT JOIN command which works just fine:
SELECT t1.avg_temperature as T_aver,
t2.new_confirmed as count
FROM 3_day_avg as t1
LEFT JOIN table2 as t2 on t1.date = t2.date
And this works great to make this table:
T_aver |count|
-----------------
-0.2 | 2 |
3 | 2 |
5 | 1 |
-2.3 | 4 |
22 | 0 |
But now I want to take it one step further and group by ranges of T_aver (bins like 0-5, 6-10, 11-15, etc) and SUM() the count column. For example, If I was to place the range on the LEFT JOIN table example above of -10 to 0, and 0 to 30, the final table would look like this:
Trange |count|
-----------------
-10 - 0 | 6 |
0 - 30 | 3 |
This above transformation is where I am stumped and I fear to make my life simpler I just need to create one big table instead...
Thanks in advance

Answer 1

You were very close! Just start with your existing query and then wrap it.
For your bins use another lookup table if you don't want to be bound to a fixed interval:
bins:
mintemp | maxtemp
-10 | 0
0 | 30
I will use num instead of count, as I never use reserved words as columns:
SELECT
CONCAT(mintemp, ' - ', maxtemp) AS Trange,
SUM(baseview.num) AS num
FROM bins
INNER JOIN (
SELECT
t1.avg_temperature as T_aver,
t2.new_confirmed as num
FROM 3_day_avg as t1
LEFT JOIN table2 as t2 on t1.date = t2.date
) AS baseview
ON baseview.T_aver>bins.mintemp AND baseview.T_aver<=bins.maxtemp
GROUP BY bins.mintemp;

Answer 2

SELECT ranges.caption Trange,
SUM(t2.new_confirmed) as `count`
FROM 3_day_avg as t1
LEFT JOIN table2 as t2 on t1.date = t2.date
JOIN ( SELECT -10 t_from, 0 t_to, '-10 - 0' caption
UNION ALL
SELECT 0, 30, '0 - 30' ) ranges ON t1.avg_temperature >= ranges.t_from
AND t1.avg_temperature < ranges.t_to
GROUP BY ranges.caption;
It is better to create static ranges table instead of dynamically generated. This allows to create and to store a lot of pre-defined sets of ranges.

Answer 3

You can group by a CASE expression which contains your bins:
SELECT
CASE
WHEN t1.avg_temperature >= -10 and t1.avg_temperature <= 0 THEN '-10 - 0'
WHEN t1.avg_temperature > 0 and t1.avg_temperature <=30 THEN '0 - 30'
END AS Trange,
SUM(t2.new_confirmed) AS count
FROM 3_day_avg AS t1 LEFT JOIN table2 AS t2
ON t1.date = t2.date
GROUP BY Trange
You may add more bins in the CASE expression, change the ranges and the inequality signs to suit your requirement.