diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
index 1305216be2..75e959045e 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
@@ -5,20 +5,24 @@ require "active_support/deprecation"
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
     module DatabaseLimits
+      def max_identifier_length # :nodoc:
+        64
+      end
+
       # Returns the maximum length of a table alias.
       def table_alias_length
-        255
+        max_identifier_length
       end
 
       # Returns the maximum length of a column name.
       def column_name_length
-        64
+        max_identifier_length
       end
       deprecate :column_name_length
 
       # Returns the maximum length of a table name.
       def table_name_length
-        64
+        max_identifier_length
       end
       deprecate :table_name_length
 
@@ -33,7 +37,7 @@ module ActiveRecord
 
       # Returns the maximum length of an index name.
       def index_name_length
-        64
+        max_identifier_length
       end
 
       # Returns the maximum number of columns per table.
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
index a1f90a0642..ad3a8d1fd9 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
@@ -121,6 +121,10 @@ module ActiveRecord
           sql
         end
 
+        def table_alias_length
+          256 # https://dev.mysql.com/doc/refman/8.0/en/identifiers.html
+        end
+
         private
           CHARSETS_OF_4BYTES_MAXLEN = ["utf8mb4", "utf16", "utf16le", "utf32"]
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 0ed4e61d18..f8c2e48808 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -400,8 +400,6 @@ module ActiveRecord
       def max_identifier_length
         @max_identifier_length ||= query_value("SHOW max_identifier_length", "SCHEMA").to_i
       end
-      alias table_alias_length max_identifier_length
-      alias index_name_length max_identifier_length
 
       # Set the authorized user for this session
       def session_auth=(user)
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index 910c6b3214..801e312658 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -319,12 +319,11 @@ module ActiveRecord
 
         group_aliases = group_fields.map { |field|
           field = connection.visitor.compile(field) if Arel.arel_node?(field)
-          column_alias_for(field)
+          column_alias_for(field.to_s.downcase)
         }
         group_columns = group_aliases.zip(group_fields)
 
-        aggregate_alias = "#{operation}_#{column_name.to_s.downcase}"
-        aggregate_alias = column_alias_for(aggregate_alias) unless aggregate_alias.match?(/\A\w+\z/)
+        aggregate_alias = column_alias_for("#{operation}_#{column_name.to_s.downcase}")
 
         select_values = [
           operation_over_aggregate_column(
@@ -369,7 +368,7 @@ module ActiveRecord
         end]
       end
 
-      # Converts the given keys to the value that the database adapter returns as
+      # Converts the given field to the value that the database adapter returns as
       # a usable column name:
       #
       #   column_alias_for("users.id")                 # => "users_id"
@@ -377,7 +376,9 @@ module ActiveRecord
       #   column_alias_for("count(distinct users.id)") # => "count_distinct_users_id"
       #   column_alias_for("count(*)")                 # => "count_all"
       def column_alias_for(field)
-        column_alias = field.to_s.downcase
+        return field if field.match?(/\A\w{,#{connection.table_alias_length}}\z/)
+
+        column_alias = +field
         column_alias.gsub!(/\*/, "all")
         column_alias.gsub!(/\W+/, " ")
         column_alias.strip!
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index c4070fc341..16c2a3661d 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -363,6 +363,17 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 60,  c[2]
   end
 
+  def test_should_calculate_grouped_with_longer_field
+    field = "a" * Account.connection.max_identifier_length
+
+    Account.update_all("#{field} = credit_limit")
+
+    c = Account.group(:firm_id).sum(field)
+    assert_equal 50,  c[1]
+    assert_equal 105, c[6]
+    assert_equal 60,  c[2]
+  end
+
   def test_should_calculate_with_invalid_field
     assert_equal 6, Account.calculate(:count, "*")
     assert_equal 6, Account.calculate(:count, :all)
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index ead4de2a13..548671045b 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -19,6 +19,7 @@ ActiveRecord::Schema.define do
     t.references :firm, index: false
     t.string  :firm_name
     t.integer :credit_limit
+    t.integer "a" * max_identifier_length
   end
 
   create_table :admin_accounts, force: true do |t|