BUG #18552: slow query, but using union is ok.

The following bug has been logged on the website:

Bug reference:      18552
Logged by:          Li Yunfeng
Email address:      yunfeng.li.nb@gmail.com
PostgreSQL version: 16.3
Operating system:   CENTOS 7
Description:

slow, waiting for a long time not return:
select a.c_mrid,a.c_pathname from sjzx_breaker a
  where (exists(select * from sjzx_disconnector b,sjzx_transformerwinding
c
    where c.c_powertransformer='117093590563292490' and
(b.c_i_node=c.c_i_node or b.c_j_node=c.c_i_node)
    and (b.c_i_node=a.c_i_node or b.c_i_node=a.c_j_node or
b.c_j_node=a.c_i_node or b.c_j_node=a.c_j_node)))
 or exists(select * from sjzx_transformerwinding f
   where f.c_powertransformer='117093590563292490' and
(f.c_i_node=a.c_i_node or f.c_i_node=a.c_j_node))

but using union, it is ok:
select a.c_mrid,a.c_pathname from sjzx_breaker a
  where (exists(select * from sjzx_disconnector b,sjzx_transformerwinding
c
    where c.c_powertransformer='117093590563292490' and
(b.c_i_node=c.c_i_node or b.c_j_node=c.c_i_node)
    and (b.c_i_node=a.c_i_node or b.c_i_node=a.c_j_node or
b.c_j_node=a.c_i_node or b.c_j_node=a.c_j_node)))
union 
select e.c_mrid,e.c_pathname from sjzx_breaker e where exists(select * from
sjzx_transformerwinding f
   where f.c_powertransformer='117093590563292490' and
(f.c_i_node=e.c_i_node or f.c_i_node=e.c_j_node))