我有以下查询,我想知道 CASE 构造有多糟糕,它强制 DB 引擎用 E.EAOpID 不为空时已经包含的值覆盖 E.EAOpID
UPDATE E
SET E.EAOpID = CASE
WHEN E.EAOpID IS NULL THEN @operationID
ELSE E.EAOpID
END,
E.AverageCapacity = E.AverageCapacity + 1,
E.Average = E.Average - (E.Average - E.Value) / E.AverageCapacity
FROM
(
SELECT E.EAOpID, E.AverageCapacity, E.Average, P.Value
FROM Probes AS P
INNER JOIN Estimates AS E ON P.EstimateID = E.ID
WHERE P.EAOpID = @operationID
) AS E;
也许将这个更新分成两个更新更便宜:
1
UPDATE E
SET E.EAOpID = @operationID
FROM
(
SELECT E.EAOpID, E.AverageCapacity, E.Average, P.Value
FROM Probes AS P
INNER JOIN Estimates AS E ON P.EstimateID = E.ID
WHERE P.EAOpID = @operationID
AND E.EAOpID IS NULL -- Additional statement here
) AS E;
2
UPDATE E
SET E.AverageCapacity = E.AverageCapacity + 1,
E.Average = E.Average - (E.Average - E.Value) / E.AverageCapacity
FROM
(
SELECT E.EAOpID, E.AverageCapacity, E.Average, P.Value
FROM Probes AS P
INNER JOIN Estimates AS E ON P.EstimateID = E.ID
WHERE P.EAOpID = @operationID
) AS E;