select cast (pkey.rdb$relation_name as varchar(31)) as pktable_name,
cast (pseg.rdb$field_name as varchar(31)) as pkcolumn_name,
  cast (fkey.rdb$relation_name as varchar(31)) as fktable_name,
  cast (fseg.rdb$field_name as varchar(31)) as fkcolumn_name,
  cast (pseg.rdb$field_position+1 as smallint) as key_seq,
  cast (fkey.rdb$constraint_name as varchar(31)) as fk_name,
  cast (refc.rdb$const_name_uq as varchar(31)) as pk_name,
  pkey.rdb$constraint_type
from rdb$relation_constraints fkey
  join rdb$ref_constraints refc on fkey.rdb$constraint_name = refc.rdb$constraint_name
  join rdb$relation_constraints pkey on refc.rdb$const_name_uq = pkey.rdb$constraint_name
  join rdb$indices fidx on fkey.rdb$index_name = fidx.rdb$index_name
  join rdb$indices pidx on pkey.rdb$index_name = pidx.rdb$index_name
  join rdb$index_segments fseg on fidx.rdb$index_name = fseg.rdb$index_name
  join rdb$index_segments pseg on pidx.rdb$index_name = pseg.rdb$index_name
   and pseg.rdb$field_position = fseg.rdb$field_position
where
   pkey.rdb$relation_name = 'TCASSOCIES'
   and pkey.rdb$constraint_type = 'PRIMARY KEY'
   and fkey.rdb$constraint_type = 'FOREIGN KEY'
--  and fkey.rdb$relation_name = 'TCASSOCIES'
order by pkey.rdb$relation_name, fkey.rdb$relation_name, pseg.rdb$field_position;

PLAN SORT (JOIN (FKEY NATURAL, REFC INDEX (RDB$INDEX_13), FIDX INDEX (RDB$INDEX_5), 
PKEY INDEX (RDB$INDEX_12), PIDX INDEX (RDB$INDEX_5), FSEG INDEX (RDB$INDEX_6), PSEG INDEX 
(RDB$INDEX_6)))

Current memory = 14298640
Delta memory = 1176
Max memory = 14781088
Elapsed time= 0.50 sec
Buffers = 3000
Reads = 0
Writes 0
Fetches = 14788