如何从SQL中的不同列中查找第一,第二和第三大值

Question

嗨我有一个包含J1,J2,J3,J4,J5,J6,J7列的表格.我想从这些列中找到最大的3个值,如L1,L2,L3.

我尝试了下面的查询来找到第一个最大的

SELECT (
    SELECT Max(v) FROM (
        VALUES 
          ([J1]), ([J2]), 
          ([J3]), ([J4]),
          ([J5]), ([J6]),
          ([J7])
    ) AS value(v)
) as [L1]FROM dbo.JTable

Answer 1

如果您的表有PK,id那么您可以使用员工的查询UNPIVOT:

SELECT *
FROM (
  SELECT *, 
         ROW_NUMBER() OVER (PARTITION BY id ORDER BY Val) AS rn
  FROM JTable
  UNPIVOT (
     Val FOR Col IN (J1, J2, J3, J4, J5, J6, J7)) AS unpvt) AS t
WHERE t.rn <= 3

如果您想要每行一行id,则可以使用PIVOT撤消UNPIVOT操作:

SELECT id, [1], [2], [3]
FROM (
  SELECT id, Val, rn
  FROM (
    SELECT id, Val, Col,
           ROW_NUMBER() OVER (PARTITION BY id ORDER BY Val) AS rn
    FROM JTable
    UNPIVOT (
       Val FOR Col IN (J1, J2, J3, J4, J5, J6, J7)) AS unpvt) AS t
  WHERE t.rn <= 3) AS src
PIVOT (
   MAX(Val) FOR rn IN ([1], [2], [3])) AS pvt