How to group by week in postgresql

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I've a database table commits with the following columns:

id | author_name | author_email | author_date (timestamp) | total_lines

Sample contents are: 

1 | abc | abc@xyz.com | 2013-03-24 15:32:49 | 1234
2 | abc | abc@xyz.com | 2013-03-27 15:32:49 | 534
3 | abc | abc@xyz.com | 2014-05-24 15:32:49 | 2344
4 | abc | abc@xyz.com | 2014-05-28 15:32:49 | 7623

I want to get a result as follows: 

id | name | week | commits
1  | abc  | 1    | 2
2  | abc  | 2    | 0

I searched online for similar solutions but couldnt get any helpful ones.

I tried this query: 

SELECT      date_part('week', author_date::date) AS weekly,
        COUNT(author_email)           
FROM        commits
GROUP BY    weekly
ORDER BY weekly

But its not the right result.

postgresql sql
2 Answers

If you want the count of all the intermediate weeks as well where there are no commits/records, you can get it by providing a start_date and end_date to generate_series() function

SELECT t1.year_week week, 
       t2.commit_count 
FROM   (SELECT week, 
               To_char(week, 'IYYY-IW') year_week 
        FROM   generate_series('2020-02-01 06:06:51.25+00'::DATE, 
               '2020-04-05 12:12:33.25+00':: 
               DATE, '1 week'::interval) AS week) t1 
       LEFT OUTER JOIN (SELECT To_char(author_date, 'IYYY-IW') year_week, 
                               COUNT(author_email)             commit_count 
                        FROM   commits 
                        GROUP  BY year_week) t2 
                    ON t1.year_week = t2.year_week;

The output will be:

     week | commit_count  
----------+-------------
2020-05   | 2
2020-06   | NULL  
2020-07   | 1
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