您需要将查询 Package 在派生表中，以便能够访问列别名

select *
from (
  SELECT 1000000 AS number
  UNION ALL
  SELECT 541 AS number
  UNION ALL
  SELECT -500 AS number
  UNION ALL
  SELECT 100 AS number
)
WHERE number = 1000000

但是要找到最大的数字，可以使用order by和limit：

select *
from (
  SELECT 1000000 AS number
  UNION ALL
  SELECT 541 AS number
  UNION ALL
  SELECT -500 AS number
  UNION ALL
  SELECT 100 AS number
)
order by number desc 
limit 1

或者，您也可以使用VALUES子句来简化此操作：

select *
from (
  values (1000000),(541),(-500),(100)
) as t(number)
order by number desc 
limit 1

您可以将公共表表达式与FETCH一起使用，如下所示：

WITH CTE_Number AS (
SELECT 1000000 AS number
UNION ALL
SELECT 541 AS number
UNION ALL
SELECT -500 AS number
UNION ALL
SELECT 100 AS number
    )
SELECT Number,'Biggest' as result
FROM CTE_Number
ORDER BY Number DESC
FETCH FIRST ROW ONLY;