SQL Server 2017

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create table tbl (account int, source varchar(20), Sep int, Oct int, Nov int);

insert into tbl values (1, 'Forecast', 110, 230, 310), (1, 'Result', 130, NULL, NULL) 
, (2, 'Forecast', 190, 440, 590), (2, 'Result', 200, NULL, NULL);
4 rows affected

SELECT account
     , COALESCE(MAX(CASE WHEN source = 'Result' THEN Sep END), MAX(CASE WHEN source = 'Forecast' THEN Sep END)) "Sep"
     , COALESCE(MAX(CASE WHEN source = 'Result' THEN Oct END), MAX(CASE WHEN source = 'Forecast' THEN Oct END)) "Sep"
     , COALESCE(MAX(CASE WHEN source = 'Result' THEN Nov END), MAX(CASE WHEN source = 'Forecast' THEN Nov END)) "Sep"
FROM tbl
GROUP BY account


account
Sep
Sep
Sep


1
130
230
310

2
200
440
590


Warning: Null value is eliminated by an aggregate or other SET operation.


SELECT t.account, COALESCE(t.r_Sep, t.f_Sep) "Sep"
     , COALESCE(t.r_Oct, t.f_Oct) "Oct"
	 , COALESCE(t.r_Nov, t.f_Nov) "Nov"
FROM (SELECT account
           , MAX(CASE WHEN source = 'Result' THEN Sep END) "r_Sep"
           , MAX(CASE WHEN source = 'Forecast' THEN Sep END) "f_Sep"
           , MAX(CASE WHEN source = 'Result' THEN Oct END) "r_Oct"
           , MAX(CASE WHEN source = 'Forecast' THEN Oct END) "f_Oct"
           , MAX(CASE WHEN source = 'Result' THEN Nov END) "r_Nov"
           , MAX(CASE WHEN source = 'Forecast' THEN Nov END) "f_Nov"
      FROM tbl
      GROUP BY account) t


account
Sep
Oct
Nov


1
130
230
310

2
200
440
590


Warning: Null value is eliminated by an aggregate or other SET operation.