Another powerful SQL skill is understanding how to group rows together by column values. Once the data is grouped together, it can be difficult to understand how to actually work with the groupings. In this lesson, we will use the group by clause, as well as the count, sum, avg, min, and max aggregate functions.
SELECT u.total, u.create_date, first_name FROM Users us INNER JOIN (SELECT count(create_date) AS total, create_date FROM Users GROUP BY create_date) u ON u.create_date = us.create_date;
SELECT create_date, first_name FROM Users WHERE create_date = (select min(create_date) FROM Users);
https://www.postgresql.org/docs/9.5/functions-aggregate.html https://dev.mysql.com/doc/refman/8.0/en/group-by-functions.html https://docs.microsoft.com/en-us/sql/t-sql/functions/aggregate-functions-transact-sql https://docs.oracle.com/database/121/SQLRF/functions003.htm