Question

I have the following mysql statement basically doing what I want it to do except for one thing.

SELECT 
a.tmc, w.date, ROUND(AVG(a.surface_temperature), 0) surface_temperature, ROUND(AVG(a.air_temperature), 0) air_temperature, 
ROUND(AVG(a.material_rate),0) material_rate, 
Time_Format(w.time, '%H:00') as time, 
ROUND(AVG(w.intensity), 0) intensity, 
FROM application a 
LEFT OUTER JOIN weather w ON a.DATE = w.DATE AND a.tmc = w.tmc 
WHERE w.DATE = '" & calendar1.SelectedDate & "' 
AND w.event= '" & weatherType.SelectedItem.Value & "' 
AND w.City = '" & sender.CssClass & "' 
GROUP BY time

This Produces:

This is fine but the problem is there are multiple TMCs per location (Think of TMC’s as fire stations in city. Big Cities have multiple TMCs

What I need it to do is average everything like it does per hour but do it for every tmc, not just the first tmc that comes up based off the time and other filtered criteria.

I attmped both:

GROUP BY TIME AND TMC

and

GROUP BY TMC

but they both provide only 1 time and the 1 location.

How do I need to tweak this statement so it pulls the average of all this criteria per hour per tmc?

I want something with the following output:

Time TMC       Temp
4:00 107+4807   27
4:00 108+3352   32
5:00 107+4807   28
5:00 105+2274   28

I hop this makes sense

Answer 1

I think you need to comma-separate them:

GROUP BY time, tmc

It’s perhaps not that clear in the manual page for the SELECT statement:

[GROUP BY {col_name | expr | position}
      [ASC | DESC], ... [WITH ROLLUP]]

i.e., you can specify multiple columns to form more granular groups.

When you specify a logical combination like

GROUP BY TIME AND TMC

things might appear to work, but the groups produced will depend on the ‘logical’ value of time and tmc – you’ll get a group for the rows where both appear ‘true’ and a group for everything else.