Sql 传递参数时过滤a，不传递参数时返回all

当我传递参数时，如何从查询中筛选记录，当参数有空值时，如何返回所有记录

SELECT nfv.Company_id, COUNT(1) as NegativeFeedback,SUM(allocated_score) as ScoreSum
FROM dbo.NegativeFeedbackView nfv
WHERE ISNULL(nfv.comp_nature_id,0) = @compNatureId 
GROUP BY nfv.Company_id

---

下面是一个示例过程，它使用可选参数进行筛选

CREATE PROCEDURE USP_MyProc(@FilterParameter AS VARCHAR(100) = NULL)

BEGIN

SELECT nfv.Company_id, COUNT(1) as NegativeFeedback,SUM(allocated_score) as ScoreSum
FROM dbo.NegativeFeedbackView nfv

WHERE
(@compNatureId  IS NULL OR ISNULL(nfv.comp_nature_id,0)= @compNatureId )

GROUP BY nfv.Company_id

END

---

使用

IF/ELSE

：

e、 g

尝试将这些情况合并到单个查询中：

SELECT nfv.Company_id, COUNT(1) as NegativeFeedback,SUM(allocated_score) as ScoreSum
FROM dbo.NegativeFeedbackView nfv
WHERE ISNULL(nfv.comp_nature_id,0) = @compNatureId 
OR @compNatureId IS NULL
GROUP BY nfv.Company_id

很可能会产生次优计划，并且它不能使用

comp\u nature\u id

上的任何索引（如果存在）

SELECT nfv.Company_id, COUNT(1) as NegativeFeedback,SUM(allocated_score) as ScoreSum
FROM dbo.NegativeFeedbackView nfv
WHERE ISNULL(nfv.comp_nature_id,0) = @compNatureId 
OR @compNatureId IS NULL
GROUP BY nfv.Company_id