Generate date series for each id

Question

I have a table with four columns. I want to create a date column with 1 day interval for each id from its date1 till date3. If no date3 then till date2, if no date2, then only date1.

How can I achieve this in Postgres? Thanks!

Sample data:

+-------+---------------------+---------------------+---------------------+
|  id   |        date1        |        date2        |        date3        |
+-------+---------------------+---------------------+---------------------+
| 76efg | 2021-01-03 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03 |
| b67cs | 2021-01-09 03:45:24 | 2021-01-14 06:55:13 |                     |
| fsf56 | 2021-01-25 11:18:03 | 2021-01-25 11:18:03 |                     |
| ghl56 | 2021-01-29 14:25:57 | 2021-02-02 17:37:10 | 2021-02-18 01:13:37 |
| 90tum | 2021-02-18 06:13:30 |                     |                     |
+-------+---------------------+---------------------+---------------------+

Desired output for id '76efg':

+-------+--------------+---------------------+---------------------+---------------------+--+
|  id   | date_created |        date1        |        date2        |        date3        |  |
+-------+--------------+---------------------+---------------------+---------------------+--+
| 76efg | 2021-01-03   | 2021-01-03 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03 |  |
| 76efg | 2021-01-04   | 2021-01-03 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03 |  |
| 76efg | 2021-01-05   | 2021-01-03 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03 |  |
| 76efg | 2021-01-06   | 2021-01-03 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03 |  |
| 76efg | 2021-01-07   | 2021-01-03 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03 |  |
| 76efg | 2021-01-08   | 2021-01-03 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03 |  |
+-------+--------------+---------------------+---------------------+---------------------+--+

Answer 1

Have you tried using generated_series()? The following query generates a series of timestamps based on date1,date2 and date3, and the limit of the series found using COALESCE - basically checks if a column is null .

WITH j (id,date1,date2,date3) AS (
  VALUES ('76efg',
          '2021-01-03 06:33:54'::TIMESTAMP,
          '2021-01-07 05:19:03'::TIMESTAMP,
          '2021-01-08 05:19:03'::TIMESTAMP ),
         ('b67cs',
         '2021-01-09 03:45:24'::TIMESTAMP,
         '2021-01-14 06:55:13'::TIMESTAMP,
         NULL),
         ('90tum','2021-02-18 06:13:30'::TIMESTAMP,
         NULL,NULL)
)
SELECT 
  id,
  generate_series(
    date1,
    COALESCE(date3,date2,date1),'1 day'::INTERVAL) AS date_created,
  date2,
  date3
FROM j;

  id   |    date_created     |        date2        |        date3        
-------+---------------------+---------------------+---------------------
 76efg | 2021-01-03 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03
 76efg | 2021-01-04 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03
 76efg | 2021-01-05 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03
 76efg | 2021-01-06 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03
 76efg | 2021-01-07 06:33:54 | 2021-01-07 05:19:03 | 2021-01-08 05:19:03
 b67cs | 2021-01-09 03:45:24 | 2021-01-14 06:55:13 | 
 b67cs | 2021-01-10 03:45:24 | 2021-01-14 06:55:13 | 
 b67cs | 2021-01-11 03:45:24 | 2021-01-14 06:55:13 | 
 b67cs | 2021-01-12 03:45:24 | 2021-01-14 06:55:13 | 
 b67cs | 2021-01-13 03:45:24 | 2021-01-14 06:55:13 | 
 b67cs | 2021-01-14 03:45:24 | 2021-01-14 06:55:13 | 
 90tum | 2021-02-18 06:13:30 |                     | 

Check this db<>fiddle.

Thanks @clamp for the hint regarding COALESCE:

COALESCE(COALESCE(date3,date2),date1) is equivalent to COALESCE(date3,date2,date1)