New version of the proposed solution, Oracle

Language: Layout:

drop table table1 
\\
drop table table2
\\

create table table1 (
  EMPLID number(10),
  XX_EMPLID varchar2(10),
  GTN   number(10),
  DEDCD  varchar2(10),
  EFFDT  date
)
\\
 
create table table2 (
  EMPLID number(10),
  DEDCD  varchar2(10),
  EFFDT  date
)
\\

insert into table1 (  EMPLID, XX_EMPLID, GTN ,  DEDCD,   EFFDT)
 values ( 1,  'A1' ,       101,   'XXYA' ,    to_date('2016-10-02','YYYY-MM-DD'))
\\

insert into table1
(  EMPLID, XX_EMPLID, GTN ,  DEDCD,   EFFDT)
values (    1,     'A1' ,       102,   'XXYY' ,    to_date('2016-10-02','YYYY-MM-DD'))
\\
     
insert into table1 (  EMPLID, XX_EMPLID, GTN ,  DEDCD,   EFFDT)
 values ( 1,  'A1' ,       103,   'XXYZ' ,    to_date('2016-10-02','YYYY-MM-DD'))
\\

insert into table2 (EMPLID , DEDCD,    EFFDT)
 values (1,      'XXYA',   to_date('2016-10-02','YYYY-MM-DD'))
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insert into table2 (EMPLID , DEDCD,    EFFDT)
 values (1,      'XXYZ',   to_date('2016-10-02','YYYY-MM-DD'))
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SELECT a.EMPLID,a.DEDCD, to_char(a.EFFDT,'YYYY-MM-DD') EFFDT, b.DEDCD as DEDCD2,GTN
   FROM 
   (
   select  t1.EFFDT,t1.GTN,t1.EMPLID,t1.DEDCD,
        row_number() over (partition by t1.EMPLID order by case when t2.EMPLID is not null then 0 else 1 end asc, t1.DEDCD) rn
 from table1 t1 left join (select distinct EMPLID,   EFFDT, DEDCD from    table2) t2 on  t1.EMPLID=t2.EMPLID AND t1.EFFDT=t2.EFFDT  and t1.DEDCD=t2.DEDCD
       ) A
    LEFT OUTER JOIN 
    (
   select  t2.EFFDT,t2.EMPLID,t2.DEDCD,
        row_number() over (partition by t2.EMPLID order by case when t1.EMPLID is not null then 0 else 1 end asc, t2.DEDCD) rn
 from table2 t2  left join (select distinct EMPLID,   EFFDT, DEDCD from    table1) t1 on  t1.EMPLID=t2.EMPLID AND t1.EFFDT=t2.EFFDT and t1.DEDCD=t2.DEDCD
    ) B
 ON ( A.EMPLID=B.EMPLID AND A.EFFDT=B.EFFDT AND a.rn=b.rn)
\\


absolute service time: 0,94 sec