To perform a sum calculation over the array of elements, use to_a.sum(&block).

Please check the discussion in f9cb645d
for more context.

This reverts commit f9cb645d.

Conflicts:
	activerecord/CHANGELOG.md

Revert "Allow blocks for count with ActiveRecord::Relation. Document and test that sum allows blocks"

This reverts commit 9cc2bf69.

Conflicts:
	activerecord/lib/active_record/relation/calculations.rb

Closes #7551

Fix build issue with postgresql.

Execute_grouped_calculation is one of those places where
ActiveRecord forgets that it has ARel underpinnings, and
assumes that the values provided to group_values are
strings. This artificially hobbles otherwise functional
code. This patch stops assuming that incoming values
respond to to_sym, stops using string interpolation for
table aliases on objects that support aliasing, and stops
unnecessarily joining group_values on the relation.

Additionally, it calls to_sql, if available, on objects
sent to column_alias_for, in order to get a more reasonable
alias string than a non-string's default to_str method.

Ensure it works with mix of symbols and strings, and with a select
clause possibly containing more than one column.

Also remove support for pluck with an array of columns, in favor of
passing the list of attributes:

    Model.pluck(:a, :b)

See comments: https://github.com/rails/rails/pull/6500#issuecomment-6030292

Also use if/else block to not use short circuit return

Fix #5990

Thanks @splattael.

Add Changelog entry. Closes #4003

This reverts commit fa6d921e.

Reason: Not a fan of such massive changes. We usually close such changes
if made to Rails master as a pull request. Following the same principle
here and reverting.

[ci skip]

For future reference, this is the regex I used: ^\s*#\s*\n(?!\s*#). Replace
with the first match, and voilà! Note that the regex matches a little bit too
much, so you probably want to `git add -i .` and go through every single diff
to check if it actually should be changed.

an alias is provided.  Without the alias, the column cannot be found
and properly typecast.