SQL Server 2016

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CREATE TABLE Dataset1
    ([TableName] varchar(10), [RowCount] int)
;
    
INSERT INTO Dataset1
    ([TableName], [RowCount])
VALUES
    ('Table1', 12),
    ('Table2', 15),
    ('Table3', 18);

CREATE TABLE Dataset2
   ([TableName] varchar(10), [RowCount] int)
;
    
INSERT INTO Dataset2
    ([TableName], [RowCount])
VALUES
    ('Table1', 12),
    ('Table6', 15),
    ('Table3', 10);
6 rows affected

SELECT ISNULL(d1.TableName,d2.TableName) as TableName,
      d1.[RowCount],
      d2.[RowCount]
FROM Dataset1 as d1
        FULL JOIN Dataset2 as d2
              ON d1.TableName = d2.TableName
WHERE
    ISNULL(d1.[RowCount],0) <> ISNULL(d2.[RowCount],0);


TableName
RowCount
RowCount


Table2
15
null

Table3
18
10

Table6
null
15


select a.tableName,
       max(case when a.src = 1 then a.[rowCount] else Null end) as rowCount1,
       max(case when a.src = 2 then a.[rowCount] else Null end) as rowCount2
from
(
(select * ,1 as src from dataset1 except select * ,1 as src from dataset2)
union all
(select * ,2 as src from dataset2 except select * , 2 as src from dataset1)
  )a
group by a.tableName


tableName
rowCount1
rowCount2


Table2
15
null

Table3
18
10

Table6
null
15


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