Refactor SQL queries (#29113)

- Updated `GROUP BY` clause to include `users.name` for adherence to
  best practices.
- Modified `HAVING` clause to reference `COUNT(posts.id)` directly
  instead of the alias `posts_written` aligning with the SQL execution
  order, as column aliases are not available during the HAVING phase.

databases/databases/databases_and_sql.md

@@ -101,9 +101,10 @@ Now we're getting into the fun stuff.  Aggregate functions like `COUNT` which re
   SELECT users.id, users.name, COUNT(posts.id) AS posts_written
   FROM users
   JOIN posts ON users.id = posts.user_id
-  GROUP BY users.id;
+  GROUP BY users.id, users.name;
 ```
 
+Note that grouping by `users.name` in addition to `users.id` improves clarity and aligns with best practices by explicitly including all selected non-aggregated columns in the `GROUP BY` clause, though it might not be strictly necessary for most databases.
 See [W3Schools' browser-based SQL playground](http://www.w3schools.com/sql/trysql.asp?filename=trysql_select_groupby) for an interactive visual.
 
 The last nifty trick is if you want to only display a subset of your data.  In a normal situation, you'd use a `WHERE` clause to narrow it down.  But if you've used an aggregate function like `COUNT` (say to get the count of posts written for each user in the example above), `WHERE` won't work anymore.  <span id='having-function'>So to conditionally retrieve records based on aggregate functions, you use the `HAVING` function, which is essentially the `WHERE` for aggregates</span>.  So say you only want to display users who have written more than 10 posts:
@@ -112,8 +113,8 @@ The last nifty trick is if you want to only display a subset of your data.  In a
   SELECT users.id, users.name, COUNT(posts.id) AS posts_written
   FROM users
   JOIN posts ON users.id = posts.user_id
-  GROUP BY users.id
-  HAVING posts_written >= 10;
+  GROUP BY users.id, users.name
+  HAVING COUNT(posts.id) >= 10;
 ```
 
 Try going back to [W3Schools' browser-based SQL playground](http://www.w3schools.com/sql/trysql.asp?filename=trysql_select_groupby) and joining the `Customers` and the `Orders` tables to get the number of orders in each country and adding the line `HAVING COUNT(*) > 10;` after `GROUP BY` (and delete the extra semicolon in the previous line).