如何在SQL中有效地对一组列进行转置和求和？

+----+------+------+------+
| ID | Col1 | Col2 | Col3 |
+----+------+------+------+
|  1 |   10 |   20 |   30 |
|  2 |   40 |   50 |   60 |
|  3 |   70 |   80 |   90 |
+----+------+------+------+

SELECT 'Col1' AS Col, Col1 AS Value FROM table
UNION ALL
SELECT 'Col2' AS Col, Col2 AS Value FROM table
UNION ALL
SELECT 'Col3' AS Col, Col3 AS Value FROM table

SELECT Col, SUM(Value) AS SumValue
FROM (
    SELECT 'Col1' AS Col, Col1 AS Value FROM table
    UNION ALL
    SELECT 'Col2' AS Col, Col2 AS Value FROM table
    UNION ALL
    SELECT 'Col3' AS Col, Col3 AS Value FROM table
) AS subquery
GROUP BY Col

+------+---------+
| Col  | SumValue|
+------+---------+
| Col1 |     120 |
| Col2 |     150 |
| Col3 |     180 |
+------+---------+