sql server 存储过程中的 CASE 语句有问题 [英] Trouble with a CASE statement in a sql server stored procedure

问题描述

我刚刚开始在 sql server 中使用存储过程，并且使用得还算不错，但我现在遇到了一个我无法理解的问题.我一直在寻找答案，但老实说，我不确定我问的是对的问题.

I have just started using stored procedures in sql server and have been getting on reasonably well, but I have now come across a problem I can't understand. I have searched for an answer, but to be honest I am not sure I am asking the right question.

我的 sp 是:

ALTER PROCEDURE [FindName]
    @Square nvarchar(100) = null,
    @Location nvarchar(100) = null,
    @Name nvarchar(100) = null,
    @NormalizedName nvarchar(100) = null,
    @SharedLand int = 0,
    @FieldNumber int = 0,
    @Description nvarchar(255) = null,
    @Dwelling nvarchar(100) = null
AS

BEGIN
    SELECT * FROM [Holdings]
    WHERE 
        ([Square] LIKE @Square OR @Square IS NULL)
        AND ([Location] = @Location OR @Location IS NULL)
        AND ([Name] LIKE @Name OR @Name IS NULL)
        AND ([NormalizedName] LIKE @NormalizedName OR @NormalizedName IS NULL)
        AND ([SharedLand] = @SharedLand OR @SharedLand = 0)
        AND ([FieldNumber] = @FieldNumber OR @FieldNumber = 0)
        AND ([Description] LIKE @Description OR @Description IS NULL)
        AND ([Dwelling] LIKE @Dwelling OR @Dwelling IS NULL)
        ORDER BY
            CASE WHEN (@NormalizedName IS NOT NULL) THEN [NormalizedName]
            ELSE [No]
        END
END

对于使用任何或所有参数但不带 CASE 但使用 CASE 语句的所有 EXEC，一切正常，以下工作:

It all works fine with all EXECs using any or all parameters without the CASE but with a CASE statement, the following work:

EXEC FindName @Square = '%D%'
EXEC FindName @SharedLand = 1

但是当我尝试时:

EXEC dbo.cafgFindName @NormalizedName = '%Thomas%'

我收到错误:将 nvarchar 值Thomas"转换为数据类型 int 时转换失败.

我无法理解的是转换发生在哪里，如果这确实是问题所在.

What I can't understand is where is the conversion taking place, if indeed that is the problem.

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推荐答案

这是因为 CASE 语句必须解析为单一类型.在这种情况下(没有双关语:)你正在考虑一个 nvarchar 或一个 int(我认为 [No] 是一个 int).

This is because a CASE Statement must resolve to a single type. In this case (no pun intended :) you are considering an nvarchar OR an int (I presume [No] is an int).

请参阅此处了解更多详情:一个案例中的排序方式和不同类型

See here for more details: Order by and Different Types in a CASE

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