# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 404
def add_column(table_name, column_name, type, options = {})
  at = create_alter_table table_name
  at.add_column(column_name, type, options)
  execute schema_creation.accept at
end

Adds a new column to the named table. See ActiveRecord::ConnectionAdapters::TableDefinition#column for details of the options you can use.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 761
def add_foreign_key(from_table, to_table, options = {})
  return unless supports_foreign_keys?

  options[:column] ||= foreign_key_column_for(to_table)

  options = {
    column: options[:column],
    primary_key: options[:primary_key],
    name: foreign_key_name(from_table, options),
    on_delete: options[:on_delete],
    on_update: options[:on_update]
  }
  at = create_alter_table from_table
  at.add_foreign_key to_table, options

  execute schema_creation.accept(at)
end

Adds a new foreign key. from_table is the table with the key column, to_table contains the referenced primary key.

The foreign key will be named after the following pattern: fk_rails_<identifier>. identifier is a 10 character long string which is deterministically generated from the from_table and column. A custom name can be specified with the :name option.

Creating a simple foreign key

add_foreign_key :articles, :authors

generates:

ALTER TABLE "articles" ADD CONSTRAINT articles_author_id_fk FOREIGN KEY ("author_id") REFERENCES "authors" ("id")

Creating a foreign key on a specific column

add_foreign_key :articles, :users, column: :author_id, primary_key: :lng_id

generates:

ALTER TABLE "articles" ADD CONSTRAINT fk_rails_58ca3d3a82 FOREIGN KEY ("author_id") REFERENCES "users" ("lng_id")

Creating a cascading foreign key

add_foreign_key :articles, :authors, on_delete: :cascade

generates:

ALTER TABLE "articles" ADD CONSTRAINT articles_author_id_fk FOREIGN KEY ("author_id") REFERENCES "authors" ("id") ON DELETE CASCADE

The options hash can include the following keys:

:column

The foreign key column name on from_table. Defaults to to_table.singularize + "_id"

:primary_key

The primary key column name on to_table. Defaults to id.

:name

The constraint name. Defaults to fk_rails_<identifier>.

:on_delete

Action that happens ON DELETE. Valid values are :nullify, :cascade: and :restrict

:on_update

Action that happens ON UPDATE. Valid values are :nullify, :cascade: and :restrict

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 569
def add_index(table_name, column_name, options = {})
  index_name, index_type, index_columns, index_options = add_index_options(table_name, column_name, options)
  execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{index_columns})#{index_options}"
end

Adds a new index to the table. column_name can be a single Symbol, or an Array of Symbols.

The index will be named after the table and the column name(s), unless you pass :name as an option.

Creating a simple index

add_index(:suppliers, :name)

generates:

CREATE INDEX suppliers_name_index ON suppliers(name)

Creating a unique index

add_index(:accounts, [:branch_id, :party_id], unique: true)

generates:

CREATE UNIQUE INDEX accounts_branch_id_party_id_index ON accounts(branch_id, party_id)

Creating a named index

add_index(:accounts, [:branch_id, :party_id], unique: true, name: 'by_branch_party')

generates:

CREATE UNIQUE INDEX by_branch_party ON accounts(branch_id, party_id)

Creating an index with specific key length

add_index(:accounts, :name, name: 'by_name', length: 10)

generates:

CREATE INDEX by_name ON accounts(name(10))

add_index(:accounts, [:name, :surname], name: 'by_name_surname', length: {name: 10, surname: 15})

generates:

CREATE INDEX by_name_surname ON accounts(name(10), surname(15))

Note: SQLite doesn't support index length.

Creating an index with a sort order (desc or asc, asc is the default)

add_index(:accounts, [:branch_id, :party_id, :surname], order: {branch_id: :desc, party_id: :asc})

generates:

CREATE INDEX by_branch_desc_party ON accounts(branch_id DESC, party_id ASC, surname)

Note: MySQL doesn't yet support index order (it accepts the syntax but ignores it).

Creating a partial index

add_index(:accounts, [:branch_id, :party_id], unique: true, where: "active")

generates:

CREATE UNIQUE INDEX index_accounts_on_branch_id_and_party_id ON accounts(branch_id, party_id) WHERE active

Note: Partial indexes are only supported for PostgreSQL and SQLite 3.8.0+.

Creating an index with a specific method

add_index(:developers, :name, using: 'btree')

generates:

CREATE INDEX index_developers_on_name ON developers USING btree (name) -- PostgreSQL
CREATE INDEX index_developers_on_name USING btree ON developers (name) -- MySQL

Note: only supported by PostgreSQL and MySQL

Creating an index with a specific type

add_index(:developers, :name, type: :fulltext)

generates:

CREATE FULLTEXT INDEX index_developers_on_name ON developers (name) -- MySQL

Note: only supported by MySQL. Supported: :fulltext and :spatial on MyISAM tables.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 667
def add_reference(table_name, ref_name, options = {})
  polymorphic = options.delete(:polymorphic)
  index_options = options.delete(:index)
  type = options.delete(:type) || :integer
  foreign_key_options = options.delete(:foreign_key)

  if polymorphic && foreign_key_options
    raise ArgumentError, "Cannot add a foreign key to a polymorphic relation"
  end

  add_column(table_name, "#{ref_name}_id", type, options)
  add_column(table_name, "#{ref_name}_type", :string, polymorphic.is_a?(Hash) ? polymorphic : options) if polymorphic
  add_index(table_name, polymorphic ? %w[type id].map{ |t| "#{ref_name}_#{t}" } : "#{ref_name}_id", index_options.is_a?(Hash) ? index_options : {}) if index_options
  if foreign_key_options
    to_table = Base.pluralize_table_names ? ref_name.to_s.pluralize : ref_name
    add_foreign_key(table_name, to_table, foreign_key_options.is_a?(Hash) ? foreign_key_options : {})
  end
end

Adds a reference. The reference column is an integer by default, the :type option can be used to specify a different type. Optionally adds a _type column, if :polymorphic option is provided. add_reference and add_belongs_to are acceptable.

The options hash can include the following keys:

:type

The reference column type. Defaults to :integer.

:index

Add an appropriate index. Defaults to false.

:foreign_key

Add an appropriate foreign key. Defaults to false.

:polymorphic

Wether an additional _type column should be added. Defaults to false.

Create a user_id integer column

add_reference(:products, :user)

Create a user_id string column

add_reference(:products, :user, type: :string)

Create supplier_id, supplier_type columns and appropriate index

add_reference(:products, :supplier, polymorphic: true, index: true)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 907
def add_timestamps(table_name, options = {})
  emit_warning_if_null_unspecified(:add_timestamps, options)
  add_column table_name, :created_at, :datetime, options
  add_column table_name, :updated_at, :datetime, options
end

Adds timestamps (created_at and updated_at) columns to table_name. Additional options (like null: false) are forwarded to add_column.

add_timestamps(:suppliers, null: false)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 438
def change_column(table_name, column_name, type, options = {})
  raise NotImplementedError, "change_column is not implemented"
end

Changes the column's definition according to the new options. See ActiveRecord::ConnectionAdapters::TableDefinition#column for details of the options you can use.

change_column(:suppliers, :name, :string, limit: 80)
change_column(:accounts, :description, :text)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 451
def change_column_default(table_name, column_name, default)
  raise NotImplementedError, "change_column_default is not implemented"
end

Sets a new default value for a column:

change_column_default(:suppliers, :qualification, 'new')
change_column_default(:accounts, :authorized, 1)

Setting the default to nil effectively drops the default:

change_column_default(:users, :email, nil)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 471
def change_column_null(table_name, column_name, null, default = nil)
  raise NotImplementedError, "change_column_null is not implemented"
end

Sets or removes a +NOT NULL+ constraint on a column. The null flag indicates whether the value can be NULL. For example

change_column_null(:users, :nickname, false)

says nicknames cannot be NULL (adds the constraint), whereas

change_column_null(:users, :nickname, true)

allows them to be NULL (drops the constraint).

The method accepts an optional fourth argument to replace existing +NULL+s with some other value. Use that one when enabling the constraint if needed, since otherwise those rows would not be valid.

Please note the fourth argument does not set a column's default.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 371
def change_table(table_name, options = {})
  if supports_bulk_alter? && options[:bulk]
    recorder = ActiveRecord::Migration::CommandRecorder.new(self)
    yield update_table_definition(table_name, recorder)
    bulk_change_table(table_name, recorder.commands)
  else
    yield update_table_definition(table_name, self)
  end
end

A block for changing columns in table.

# change_table() yields a Table instance
change_table(:suppliers) do |t|
  t.column :name, :string, limit: 60
  # Other column alterations here
end

The options hash can include the following keys:

:bulk

Set this to true to make this a bulk alter query, such as

ALTER TABLE `users` ADD COLUMN age INT(11), ADD COLUMN birthdate DATETIME ...

Defaults to false.

Add a column

change_table(:suppliers) do |t|
  t.column :name, :string, limit: 60
end

Add 2 integer columns

change_table(:suppliers) do |t|
  t.integer :width, :height, null: false, default: 0
end

Add created_at/updated_at columns

change_table(:suppliers) do |t|
  t.timestamps
end

Add a foreign key column

change_table(:suppliers) do |t|
  t.references :company
end

Creates a company_id(integer) column.

Add a polymorphic foreign key column

change_table(:suppliers) do |t|
  t.belongs_to :company, polymorphic: true
end

Creates company_type(varchar) and company_id(integer) columns.

Remove a column

change_table(:suppliers) do |t|
  t.remove :company
end

Remove several columns

change_table(:suppliers) do |t|
  t.remove :company_id
  t.remove :width, :height
end

Remove an index

change_table(:suppliers) do |t|
  t.remove_index :company_id
end

See also Table for details on all of the various column transformation.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 90
def column_exists?(table_name, column_name, type = nil, options = {})
  column_name = column_name.to_s
  columns(table_name).any?{ |c| c.name == column_name &&
                                (!type                     || c.type == type) &&
                                (!options.key?(:limit)     || c.limit == options[:limit]) &&
                                (!options.key?(:precision) || c.precision == options[:precision]) &&
                                (!options.key?(:scale)     || c.scale == options[:scale]) &&
                                (!options.key?(:default)   || c.default == options[:default]) &&
                                (!options.key?(:null)      || c.null == options[:null]) }
end

Checks to see if a column exists in a given table.

# Check a column exists
column_exists?(:suppliers, :name)

# Check a column exists of a particular type
column_exists?(:suppliers, :name, :string)

# Check a column exists with a specific definition
column_exists?(:suppliers, :name, :string, limit: 100)
column_exists?(:suppliers, :name, :string, default: 'default')
column_exists?(:suppliers, :name, :string, null: false)
column_exists?(:suppliers, :tax, :decimal, precision: 8, scale: 2)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 74
def columns(table_name) end

Returns an array of Column objects for the table specified by table_name. See the concrete implementation for details on the expected parameter values.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 275
def create_join_table(table_1, table_2, options = {})
  join_table_name = find_join_table_name(table_1, table_2, options)

  column_options = options.delete(:column_options) || {}
  column_options.reverse_merge!(null: false)

  t1_column, t2_column = [table_1, table_2].map{ |t| t.to_s.singularize.foreign_key }

  create_table(join_table_name, options.merge!(id: false)) do |td|
    td.integer t1_column, column_options
    td.integer t2_column, column_options
    yield td if block_given?
  end
end

Creates a new join table with the name created using the lexical order of the first two arguments. These arguments can be a String or a Symbol.

# Creates a table called 'assemblies_parts' with no id.
create_join_table(:assemblies, :parts)

You can pass a options hash can include the following keys:

:table_name

Sets the table name overriding the default

:column_options

Any extra options you want appended to the columns definition.

:options

Any extra options you want appended to the table definition.

:temporary

Make a temporary table.

:force

Set to true to drop the table before creating it. Defaults to false.

Note that create_join_table does not create any indices by default; you can use its block form to do so yourself:

create_join_table :products, :categories do |t|
  t.index :product_id
  t.index :category_id
end

Add a backend specific option to the generated SQL (MySQL)

create_join_table(:assemblies, :parts, options: 'ENGINE=InnoDB DEFAULT CHARSET=utf8')

generates:

CREATE TABLE assemblies_parts (
  assembly_id int NOT NULL,
  part_id int NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 205
def create_table(table_name, options = {})
  td = create_table_definition table_name, options[:temporary], options[:options], options[:as]

  if options[:id] != false && !options[:as]
    pk = options.fetch(:primary_key) do
      Base.get_primary_key table_name.to_s.singularize
    end

    td.primary_key pk, options.fetch(:id, :primary_key), options
  end

  yield td if block_given?

  if options[:force] && table_exists?(table_name)
    drop_table(table_name, options)
  end

  result = execute schema_creation.accept td

  unless supports_indexes_in_create?
    td.indexes.each_pair do |column_name, index_options|
      add_index(table_name, column_name, index_options)
    end
  end

  td.foreign_keys.each do |other_table_name, foreign_key_options|
    add_foreign_key(table_name, other_table_name, foreign_key_options)
  end

  result
end

Creates a new table with the name table_name. table_name may either be a String or a Symbol.

There are two ways to work with create_table. You can use the block form or the regular form, like this:

Block form

# create_table() passes a TableDefinition object to the block.
# This form will not only create the table, but also columns for the
# table.

create_table(:suppliers) do |t|
  t.column :name, :string, limit: 60
  # Other fields here
end

Block form, with shorthand

# You can also use the column types as method calls, rather than calling the column method.
create_table(:suppliers) do |t|
  t.string :name, limit: 60
  # Other fields here
end

Regular form

# Creates a table called 'suppliers' with no columns.
create_table(:suppliers)
# Add a column to 'suppliers'.
add_column(:suppliers, :name, :string, {limit: 60})

The options hash can include the following keys:

:id

Whether to automatically add a primary key column. Defaults to true. Join tables for has_and_belongs_to_many should set it to false.

:primary_key

The name of the primary key, if one is to be added automatically. Defaults to id. If :id is false this option is ignored.

Note that Active Record models will automatically detect their primary key. This can be avoided by using self.primary_key= on the model to define the key explicitly.

:options

Any extra options you want appended to the table definition.

:temporary

Make a temporary table.

:force

Set to true to drop the table before creating it. Set to :cascade to drop dependent objects as well. Defaults to false.

:as

SQL to use to generate the table. When this option is used, the block is ignored, as are the :id and :primary_key options.

Add a backend specific option to the generated SQL (MySQL)

create_table(:suppliers, options: 'ENGINE=InnoDB DEFAULT CHARSET=utf8')

generates:

CREATE TABLE suppliers (
  id int(11) DEFAULT NULL auto_increment PRIMARY KEY
) ENGINE=InnoDB DEFAULT CHARSET=utf8

Rename the primary key column

create_table(:objects, primary_key: 'guid') do |t|
  t.column :name, :string, limit: 80
end

generates:

CREATE TABLE objects (
  guid int(11) DEFAULT NULL auto_increment PRIMARY KEY,
  name varchar(80)
)

Do not add a primary key column

create_table(:categories_suppliers, id: false) do |t|
  t.column :category_id, :integer
  t.column :supplier_id, :integer
end

generates:

CREATE TABLE categories_suppliers (
  category_id int,
  supplier_id int
)

Create a temporary table based on a query

create_table(:long_query, temporary: true,
  as: "SELECT * FROM orders INNER JOIN line_items ON order_id=orders.id")

generates:

CREATE TEMPORARY TABLE long_query AS
  SELECT * FROM orders INNER JOIN line_items ON order_id=orders.id

See also ActiveRecord::ConnectionAdapters::TableDefinition#column for details on how to create columns.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 32
def data_source_exists?(name)
  data_sources.include?(name.to_s)
end

Checks to see if the data source name exists on the database.

data_source_exists?(:ebooks)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 24
def data_sources
  tables
end

Returns the relation names useable to back Active Record models. For most adapters this means all tables and views.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 296
def drop_join_table(table_1, table_2, options = {})
  join_table_name = find_join_table_name(table_1, table_2, options)
  drop_table(join_table_name)
end

Drops the join table specified by the given arguments. See create_join_table for details.

Although this command ignores the block if one is given, it can be helpful to provide one in a migration's change method so it can be reverted. In that case, the block will be used by create_join_table.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 398
def drop_table(table_name, options = {})
  execute "DROP TABLE #{quote_table_name(table_name)}"
end

Drops a table from the database.

:force

Set to :cascade to drop dependent objects as well. Defaults to false.

Although this command ignores most options and the block if one is given, it can be helpful to provide these in a migration's change method so it can be reverted. In that case, options and the block will be used by create_table.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 715
def foreign_keys(table_name)
  raise NotImplementedError, "foreign_keys is not implemented"
end

Returns an array of foreign keys for the given table. The foreign keys are represented as ForeignKeyDefinition objects.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 61
def index_exists?(table_name, column_name, options = {})
  column_names = Array(column_name).map(&:to_s)
  index_name = options.key?(:name) ? options[:name].to_s : index_name(table_name, column: column_names)
  checks = []
  checks << lambda { |i| i.name == index_name }
  checks << lambda { |i| i.columns == column_names }
  checks << lambda { |i| i.unique } if options[:unique]

  indexes(table_name).any? { |i| checks.all? { |check| check[i] } }
end

Checks to see if an index exists on a table for a given index definition.

# Check an index exists
index_exists?(:suppliers, :company_id)

# Check an index on multiple columns exists
index_exists?(:suppliers, [:company_id, :company_type])

# Check a unique index exists
index_exists?(:suppliers, :company_id, unique: true)

# Check an index with a custom name exists
index_exists?(:suppliers, :company_id, name: "idx_company_id")

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 634
def index_name_exists?(table_name, index_name, default)
  return default unless respond_to?(:indexes)
  index_name = index_name.to_s
  indexes(table_name).detect { |i| i.name == index_name }
end

Verifies the existence of an index with a given name.

The default argument is returned if the underlying implementation does not define the indexes method, as there's no way to determine the correct answer in that case.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 835
def initialize_schema_migrations_table
  ActiveRecord::SchemaMigration.create_table
end

Should not be called normally, but this operation is non-destructive. The migrations module handles this automatically.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 13
def native_database_types
  {}
end

Returns a hash of mappings from the abstract data types to the native database types. See ActiveRecord::ConnectionAdapters::TableDefinition#column for details on the recognized abstract data types.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 428
def remove_column(table_name, column_name, type = nil, options = {})
  execute "ALTER TABLE #{quote_table_name(table_name)} DROP #{quote_column_name(column_name)}"
end

Removes the column from the table definition.

remove_column(:suppliers, :qualification)

The type and options parameters will be ignored if present. It can be helpful to provide these in a migration's change method so it can be reverted. In that case, type and options will be used by add_column.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 414
def remove_columns(table_name, *column_names)
  raise ArgumentError.new("You must specify at least one column name. Example: remove_columns(:people, :first_name)") if column_names.empty?
  column_names.each do |column_name|
    remove_column(table_name, column_name)
  end
end

Removes the given columns from the table definition.

remove_columns(:suppliers, :qualification, :experience)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 793
def remove_foreign_key(from_table, options_or_to_table = {})
  return unless supports_foreign_keys?

  if options_or_to_table.is_a?(Hash)
    options = options_or_to_table
  else
    options = { column: foreign_key_column_for(options_or_to_table) }
  end

  fk_name_to_delete = options.fetch(:name) do
    fk_to_delete = foreign_keys(from_table).detect {|fk| fk.column == options[:column].to_s }

    if fk_to_delete
      fk_to_delete.name
    else
      raise ArgumentError, "Table '#{from_table}' has no foreign key on column '#{options[:column]}'"
    end
  end

  at = create_alter_table from_table
  at.drop_foreign_key fk_name_to_delete

  execute schema_creation.accept(at)
end

Removes the given foreign key from the table.

Removes the foreign key on accounts.branch_id.

remove_foreign_key :accounts, :branches

Removes the foreign key on accounts.owner_id.

remove_foreign_key :accounts, column: :owner_id

Removes the foreign key named special_fk_name on the accounts table.

remove_foreign_key :accounts, name: :special_fk_name

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 592
def remove_index(table_name, options = {})
  remove_index!(table_name, index_name_for_remove(table_name, options))
end

Removes the given index from the table.

Removes the index_accounts_on_column in the accounts table.

remove_index :accounts, :column

Removes the index named index_accounts_on_branch_id in the accounts table.

remove_index :accounts, column: :branch_id

Removes the index named index_accounts_on_branch_id_and_party_id in the accounts table.

remove_index :accounts, column: [:branch_id, :party_id]

Removes the index named by_branch_party in the accounts table.

remove_index :accounts, name: :by_branch_party

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 702
def remove_reference(table_name, ref_name, options = {})
  if options[:foreign_key]
    to_table = Base.pluralize_table_names ? ref_name.to_s.pluralize : ref_name
    remove_foreign_key(table_name, to_table)
  end

  remove_column(table_name, "#{ref_name}_id")
  remove_column(table_name, "#{ref_name}_type") if options[:polymorphic]
end

Removes the reference(s). Also removes a type column if one exists. remove_reference, remove_references and remove_belongs_to are acceptable.

Remove the reference

remove_reference(:products, :user, index: true)

Remove polymorphic reference

remove_reference(:products, :supplier, polymorphic: true)

Remove the reference with a foreign key

remove_reference(:products, :user, index: true, foreign_key: true)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 917
def remove_timestamps(table_name, options = {})
  remove_column table_name, :updated_at
  remove_column table_name, :created_at
end

Removes the timestamp columns (created_at and updated_at) from the table definition.

remove_timestamps(:suppliers)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 479
def rename_column(table_name, column_name, new_column_name)
  raise NotImplementedError, "rename_column is not implemented"
end

Renames a column.

rename_column(:suppliers, :description, :name)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 606
def rename_index(table_name, old_name, new_name)
  validate_index_length!(table_name, new_name)

  # this is a naive implementation; some DBs may support this more efficiently (Postgres, for instance)
  old_index_def = indexes(table_name).detect { |i| i.name == old_name }
  return unless old_index_def
  add_index(table_name, old_index_def.columns, name: new_name, unique: old_index_def.unique)
  remove_index(table_name, name: old_name)
end

Renames an index.

Rename the index_people_on_last_name index to index_users_on_last_name:

rename_index :people, 'index_people_on_last_name', 'index_users_on_last_name'

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 385
def rename_table(table_name, new_name)
  raise NotImplementedError, "rename_table is not implemented"
end

Renames a table.

rename_table('octopuses', 'octopi')

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 18
def table_alias_for(table_name)
  table_name[0...table_alias_length].tr('.', '_')
end

Truncates a table alias according to the limits of the current adapter.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 40
def table_exists?(table_name)
  tables.include?(table_name.to_s)
end

Checks to see if the table table_name exists on the database.

table_exists?(:developers)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 975
def quoted_columns_for_index(column_names, options = {})
  option_strings = Hash[column_names.map {|name| [name, '']}]

  # add index sort order if supported
  if supports_index_sort_order?
    option_strings = add_index_sort_order(option_strings, column_names, options)
  end

  column_names.map {|name| quote_column_name(name) + option_strings[name]}
end

Overridden by the MySQL adapter for supporting index lengths