我正在尝试在SELECT语句中创建一个新列，该列从同一个表中选择顶级行。
示例数据：
ITEM_VALUE DESCRIPTION LEVEL_NO ITEM_ABOVE
100 Ford 3 CAR
200 Honda Own 3 CAR
210 Honda 3rd Party 3 CAR
1000 Ford 4 100
2000 Honda T Own 4 200
801 Ford 1 4 1000
802 Ford 2 4 1000
803 Ford 3 4 1000
804 Ford 4 4 1000
805 Ford 5 4 1000
806 Ford 6 4 1000
807 Ford 7 4 1000
808 Ford 8 4 1000
814 Ford 4 1000
809 Honda 4 2000
2100 Honda T 3rd Party 4 210
预期输出：
DESCRIPTION ITEM_GROUP
Ford Ford
Honda Own Honda Own
Honda 3rd Party Honda 3rd Party
Ford Ford
Honda T Own Honda Own
Ford 1 Ford
Ford 2 Ford
Ford 3 Ford
Ford 4 Ford
Ford 5 Ford
Ford 6 Ford
Ford 7 Ford
Ford 8 Ford
Ford Ford
Honda Honda Own
Honda T 3rd Party Honda 3rd Party
答案 0 :(得分：2)
您可以使用递归CTE：
WITH CTE(ITEM_VALUE, ITEM_ABOVE, DESCRIPTION, ITEM_GROUP) AS
(
SELECT ITEM_VALUE, ITEM_ABOVE, DESCRIPTION, DESCRIPTION AS ITEM_GROUP
FROM mytable
WHERE ITEM_ABOVE = 'CAR'
UNION ALL
SELECT t1.ITEM_VALUE, t1.ITEM_ABOVE, t1.DESCRIPTION, t2.ITEM_GROUP
FROM mytable t1
JOIN CTE t2 ON t1.ITEM_ABOVE = t2.ITEM_VALUE
)
SELECT ITEM_VALUE, ITEM_ABOVE, DESCRIPTION, ITEM_GROUP
FROM CTE