Fixes bugs for using indexes in CREATE TABLE by adding checks for table existence

Also:
  - updates tests by stubbing table_exists? method
  - adds entry for creating indexes in CREATE TABLE to changelog

5 files changed, 25 insertions, 6 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 6e77493de9..ccd07ce248 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,18 @@
+*   Create indexes inline in CREATE TABLE for MySQL
+
+    This is important, because adding an index on a temporary table after it has been created
+    would commit the transaction.
+    It also allows creating and dropping indexed tables with fewer queries and fewer permissions required.
+
+    Example:
+
+        create_table :temp, temporary: true, as: "SELECT id, name, zip FROM a_really_complicated_query" do |t|
+          t.index :zip
+        end
+        # => CREATE TEMPORARY TABLE temp (INDEX (zip)) AS SELECT id, name, zip FROM a_really_complicated_query
+
+    *Cody Cutrer*, *Steve Rice*
+
 *   Save `has_one` association even if the record doesn't changed.
 
     Fixes #14407.
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 59210c345f..23404a5c48 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -795,7 +795,7 @@ module ActiveRecord
           if index_name.length > max_index_length
             raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' is too long; the limit is #{max_index_length} characters"
           end
-          if index_name_exists?(table_name, index_name, false)
+          if table_exists?(table_name) && index_name_exists?(table_name, index_name, false)
             raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' already exists"
           end
           index_columns = quoted_columns_for_index(column_names, options).join(", ")
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 96c7d5d7eb..a1748c9261 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -12,7 +12,7 @@ module ActiveRecord
           statements = []
           statements.concat(o.columns.map { |c| accept c })
           statements.concat(o.indexes.map { |(column_name, options)| index_in_create(o.name, column_name, options) })
-          create_sql << "(#{statements.join(', ')}) "
+          create_sql << "(#{statements.join(', ')}) " if statements.present?
           create_sql << "#{o.options}"
           create_sql << " AS #{@conn.to_sql(o.as)}" if o.as
           create_sql
diff --git a/activerecord/test/cases/adapters/mysql/active_schema_test.rb b/activerecord/test/cases/adapters/mysql/active_schema_test.rb
index 072aa65000..35681fb5ae 100644
--- a/activerecord/test/cases/adapters/mysql/active_schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql/active_schema_test.rb
@@ -17,7 +17,8 @@ class ActiveSchemaTest < ActiveRecord::TestCase
   end
 
   def test_add_index
-    # add_index calls index_name_exists? which can't work since execute is stubbed
+    # add_index calls table_exists? and index_name_exists? which can't work since execute is stubbed
+    def (ActiveRecord::Base.connection).table_exists?(*); true; end
     def (ActiveRecord::Base.connection).index_name_exists?(*); false; end
 
     expected = "CREATE  INDEX `index_people_on_last_name`  ON `people` (`last_name`) "
@@ -118,7 +119,8 @@ class ActiveSchemaTest < ActiveRecord::TestCase
 
   def test_indexes_in_create
     begin
-      ActiveRecord::Base.connection.stubs(:index_name_exists?).returns(false)
+      ActiveRecord::Base.connection.stubs(:table_exists?).with(:temp).returns(false)
+      ActiveRecord::Base.connection.stubs(:index_name_exists?).with(:index_temp_on_zip).returns(false)
       expected = "CREATE TEMPORARY TABLE `temp` (INDEX `index_temp_on_zip` (`zip`)) ENGINE=InnoDB AS SELECT id, name, zip FROM a_really_complicated_query"
       actual = ActiveRecord::Base.connection.create_table(:temp, temporary: true, as: "SELECT id, name, zip FROM a_really_complicated_query") do |t|
         t.index :zip
diff --git a/activerecord/test/cases/adapters/mysql2/active_schema_test.rb b/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
index 91d880e5ae..925b9c1bd1 100644
--- a/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
@@ -17,7 +17,8 @@ class ActiveSchemaTest < ActiveRecord::TestCase
   end
 
   def test_add_index
-    # add_index calls index_name_exists? which can't work since execute is stubbed
+    # add_index calls table_exists? and index_name_exists? which can't work since execute is stubbed
+    def (ActiveRecord::Base.connection).table_exists?(*); true; end
     def (ActiveRecord::Base.connection).index_name_exists?(*); false; end
 
     expected = "CREATE  INDEX `index_people_on_last_name`  ON `people` (`last_name`) "
@@ -118,7 +119,8 @@ class ActiveSchemaTest < ActiveRecord::TestCase
 
   def test_indexes_in_create
     begin
-      ActiveRecord::Base.connection.stubs(:index_name_exists?).returns(false)
+      ActiveRecord::Base.connection.stubs(:table_exists?).with(:temp).returns(false)
+      ActiveRecord::Base.connection.stubs(:index_name_exists?).with(:index_temp_on_zip).returns(false)
       expected = "CREATE TEMPORARY TABLE `temp` (INDEX `index_temp_on_zip` (`zip`)) ENGINE=InnoDB AS SELECT id, name, zip FROM a_really_complicated_query"
       actual = ActiveRecord::Base.connection.create_table(:temp, temporary: true, as: "SELECT id, name, zip FROM a_really_complicated_query") do |t|
         t.index :zip