Oracle 18c

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create table T1( num_ )
as
select 1 from dual ;
1 rows affected

create table T2( num_ )
as
select 200 from dual ;
1 rows affected

select num_, '<- T1' from T1
union all
select num_, '<- T2' from T2 ;


NUM_
'<-T1'


1
<- T1

200
<- T2


begin
  if exists( select num_ from T1 where num_  = 2 ) then
    insert into T2( num_ ) values( 2 ) ;
    dbms_output.put_line( 'if' ) ;
  else
    insert into T1( num_ ) values( 2 ) ;
    insert into T2( num_ ) values( 2 ) ;
    dbms_output.put_line( 'else' ) ;
  end if ;
end ;
/
ORA-06550: line 2, column 6:
PLS-00204: function or pseudo-column 'EXISTS' may be used inside a SQL statement only
ORA-06550: line 2, column 3:
PL/SQL: Statement ignored

begin
  for x in ( select count(*) cnt
             from dual
             where exists ( select num_ from T1 where num_  = 2  ) 
  ) loop
    if ( x.cnt = 1 ) then                  -- found
      insert into T2( num_ ) values( 2 ) ;
      dbms_output.put_line( 'if' ) ;
    else                                   -- not found
      insert into T1( num_ ) values( 2 ) ;
      insert into T2( num_ ) values( 2 ) ;
      dbms_output.put_line( 'else' ) ; 
    end if;
  end loop;
end;
/
1 rows affected

dbms_output:
else

select num_, '<- T1' as table_ from T1
union all
select num_, '<- T2' from T2 ;


NUM_
TABLE_


1
<- T1

2
<- T1

200
<- T2

2
<- T2


begin
  for x in ( select count(*) cnt
             from dual
             where exists ( select num_ from T1 where num_  = 2  ) 
  ) loop
    if ( x.cnt = 1 ) then                  -- found
      insert into T2( num_ ) values( 2 ) ;
      dbms_output.put_line( 'if' ) ;
    else                                   -- not found
      insert into T1( num_ ) values( 2 ) ;
      insert into T2( num_ ) values( 2 ) ;
      dbms_output.put_line( 'else' ) ; 
    end if ;
  end loop ;
  commit ;
end ;
/
1 rows affected

dbms_output:
if

select num_, '<- T1' as table_ from T1
union all
select num_, '<- T2' from T2 ;


NUM_
TABLE_


1
<- T1

2
<- T1

200
<- T2

2
<- T2

2
<- T2