Re: Recursive Queries

[Olivier Gautherot <ogautherot@xxxxxxxxxxxxx>]

Hi Alex,

On Thu, Apr 16, 2020 at 10:36 AM Alex Magnum <magnum11200@xxxxxxxxx> wrote:

Hi,

I have a simple table with singup timestamps

What I would like to do is to create a table as shown below that displays the counts per our for the past n dates.

I can do this with a function but is there an easy way to use recursive queries?

     Counts per hour for given date

HR   2020-04-01  2020-04-02  ... 2020-04-10
00      38           33              36  
01      33           26              18
02      26           36              17
03      36           18              10
04      18           17               3
05      17           10               3
06      10            3               6
07       3            3              10
.        3            6              13
.        6           10              22
.       10           13              12
22      13           22               9
23      22           11               8

Thanks for any suggestions. 

A

You don't need subqueries. The WHEN statement can help you in this case (a bit tedious to write but fast to run):

WITH q AS (select date_part('hour', ts) AS hr, ts::date AS mydate FROM your_table_or_query)

SELECT hr,

    sum(CASE WHEN mydate = '2020-04-01'::date THEN 1 ELSE 0 END),

    sum(CASE WHEN mydate = '2020-04-02'::date THEN 1 ELSE 0 END),

    ...

FROM q ORDER BY hr;

Hope it helps

--

Olivier Gautherot

Tel: +33 6 02 71 92 23 

https://www.linkedin.com/in/ogautherot/