Question

In SQL, 3 tables joined together, retreving 3 values: value, time, value_name. Value is the one I want averaged by day, time is in datetime format on about 10 mins – this one I want it to be converted in day to day, resulting in one row for every day – and my value_name witch cand be any selected value.

Here is my syntax:

select time.entry_time, value_type.value_name, 
       avg(value.value) AVG_VALUE
FROM Value
inner join time on value.time_id = time.id
inner join value_type on value.type_id = value_type.id
WHERE value_type.value_name = 'CUSTOM'
GROUP BY DATEPART(DAY, time.entry_time)

Here I get an error:

Column time.entry_time is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Can you please help me with this syntax?

Answer 1

Two problems:

1. You select time.entry_time, but are grouping on DATEPART(DAY, time.entry_time). Which entry time do you want? Did you mean to select DATEPART(DAY, time.entry_time) instead?

2. You are not grouping by value_type.value_name. You will need to add this to the GROUP BY clause. (Yes, even though there will only be one value ‘CUSTOM’).

Try:

select DATEPART(DAY, time.entry_time), value_type.value_name, 
       avg(value.value) AVG_VALUE
FROM Value
inner join time on value.time_id = time.id
inner join value_type on value.type_id = value_type.id
WHERE value_type.value_name = 'CUSTOM'
GROUP BY DATEPART(DAY, time.entry_time), value_type.value_name