create or alter procedure SP_0
as
    declare function fn_internal_enable_reserving() returns boolean deterministic as
    begin
      return rdb$get_context('USER_SESSION', 'ENABLE_RESERVES_WHEN_ADD_INVOICE')='1';
    end
begin
  /* Procedure Text */

end

.............................................................................
            merge into tmp$perf_log t -- unit, trn_id
            using rdb$database s
            on t.unit = :a_unit  and t.trn_id = :v_curr_tx
            when MATCHED then
                update set
                    --fb_gdscode = :a_gdscode,
                    info = coalesce( info, '' ) || coalesce( trim(iif( info>'', '; ', '') || :a_info), ''),
                    dts_end = :v_dts,
                    elapsed_ms = datediff(millisecond from dts_beg to :v_dts),
                    aux1 = :a_aux1,
                    aux2 = :a_aux2
             when NOT matched then
                 insert(
                     id,
                     unit,
                     info,
                     ip,
                     trn_id,
                     dts_beg
                 )
                 values(
                     gen_id(g_perf_log,1),
                     :a_unit,
                     :a_info,
                     rdb$get_context('SYSTEM', 'CLIENT_ADDRESS'),
                     :v_curr_tx,
                     :v_dts
                 )
             returning id, dts_end, info into v_id, v_end, v_info; -- not null ==> this is FINISH of some mode
.......................................................................................................................

create or alter procedure SP0
as
begin
  merge into customer c
  using rdb$database
  on 1=1
  when matched then update set c.city = c.city;
end

create or alter procedure SP0
as
begin
  merge into customer c
  using rdb$database r
  on 1=1
  when matched then update set c.city = c.city;
end

create or alter procedure SP0
as
begin
  merge into customer c
  using rdb$database r
  on 1=1
  when matched then delete;
end

create or alter procedure SP0
as
begin
  merge into customer c
  using rdb$database r
  on 1=1
  when matched and c.city is null then update set c.city='AAA';
end