create trigger trig_ddl before any ddl statement
as
begin
   --
end

create trigger R$DDL_BeforeTouchTable BEFORE CREATE TABLE or ALTER TABLE or DROP TABLE as
begin
  if (rdb$get_context('USER_TRANSACTION', 'ParallelTransId') is null) then
    rdb$set_context('USER_TRANSACTION', 'ParallelTransId', 
      CreateTransaction(CURRENT_CONNECTION, 'isc_tpb_read_committed, isc_tpb_rec_version, isc_tpb_nowait')
    );
end;

CREATE OR ALTER trigger "R$DDL_AfterCreateTable"
active after create table position 0
AS
  declare FieldName varchar(255);
  declare TableName varchar(255);
  declare TableId integer;
  declare FieldId integer;
  declare ParallelTransactionId bigint;
  declare InParams R$TParams;
  declare ReturningValues R$TReturningValues;
begin
  TableName = rdb$get_context('DDL_TRIGGER', 'OBJECT_NAME');
  ParallelTransactionId = rdb$get_context('USER_TRANSACTION', 'ParallelTransId');
  InParams = R$CreateQueryParams;
  R$AddStrParam(InParams, 'TableName', :TableName);
  ExecQueryWithParams(ParallelTransactionId, 'insert into R$Tables (R$Name, ...) values (:TableName, ...) returning id into :TableId', InParams, ReturningValues);
  TableId = R$GetIntReturnValue(ReturningValues, 'TableId');

  InParams = R$CreateQueryParams;
  R$AddIntParam(InParams, 'TableId', :TableId);
  R$AddStrParam(InParams, 'FieldName', NULL);
  for select rdb$field_name from rdb$relation_fields where rdb$relation_name = TableName order by rdb$field_position into :FieldName do
  begin
    R$SetStrParam(InParams, 'FieldName', :FieldName);
    ExecQueryWithParams(ParallelTransactionId, 'insert into R$TableFields (R$TableId, R$Name, ...) values (:TableId, :TableName, ...)', InParams, NULL);
  end
end

CREATE OR ALTER trigger R$DDL_OnCommit
active on transaction commit position 0
AS
  declare ParallelTransactionId bigint;
begin
  ParallelTransactionId = rdb$get_context('USER_TRANSACTION', 'ParallelTransId');
  if (not (ParallelTransactionId is null)) then 
    CommitTransaction(ParallelTransactionId);
end;

CREATE OR ALTER trigger R$DDL_OnRollback
active on transaction rollback position 0
AS
  declare ParallelTransactionId bigint;
begin
  ParallelTransactionId = rdb$get_context('USER_TRANSACTION', 'ParallelTransId');
  if (not (ParallelTransactionId is null)) then 
    RollbackTransaction(ParallelTransactionId);
end