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Sum of item count in an SQL query based on DATE_TRUNC

I’ve got a table which contains event status data, similar to this:

  ID             Time               Status
------  --------------------------  ------
357920  2019-12-25 09:31:38.854764    1
362247  2020-01-02 09:31:42.498483    1
362248  2020-01-02 09:31:46.166916    1
362249  2020-01-02 09:31:47.430933    1
362300  2020-01-03 09:31:46.932333    1
362301  2020-01-03 09:31:47.231288    1

I’d like to construct a query which returns the number of successful events each day, so:

         Time              Count
-------------------------- -----
2019-12-25 00:00:00.000000   1
2020-01-02 00:00:00.000000   3
2020-01-03 00:00:00.000000   2

I’ve stumbled across this SO answer to a similar question, but the answer there is for all the data returned by the query, whereas I need the sum grouped by date range.

Also, I cannot use BETWEEN to select a specific date range, since this query is for a Grafana dashboard, and the date range is determined by the dashboard’s UI. I’m using Postgres for the SQL dialect, in case that matters.

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Answer

You need to remove the time from time component. In most databases, you can do this by converting to a date:

select cast(time as date) as dte, 
       sum(case when status = 1 then 1 else 0 end) as num_successful
from t
group by cast(time as date)
order by dte;

This assumes that 1 means “successful”.

The cast() does not work in all databases. Other alternatives are things like trunc(time), date_trunc('day', time), date_trunc(time, day) — and no doubt many others.

In Postgres, I would phrase this as:

select date_trunc('day', time) as dte, 
       count(*) filter (where status = 1) as num_successful
from t
group by dte
order by dte;
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