Question

我正在使用以下方法获取列表：

var recommend1 = db.Recommendation
    .Where(c => c.Comments != "" && 
                c.Comments != null && 
                c.Visit.ClinicId == 5)
    .Select(c => c.VisitId)
    .ToList();

这将返回0。但是，当我使用以下命令将其作为SQL测试时：

SELECT dbo.Visit.VisitId
FROM   dbo.Recommendation 
    INNER JOIN dbo.Visit ON dbo.Recommendation.VisitId = dbo.Visit.VisitId
WHERE  
    (dbo.Visit.ClinicId = '5') AND 
    (dbo.Recommendation.Comments = '') OR
    (dbo.Recommendation.Comments IS NULL)

返回3！列注释是不可为null的nvarchar（MAX）。

为什么结果不一样？

Answer 1

var recommend1 = db.Recommendation.Where(c => c.Comments != "" || c.Comments != null)
                                  .Where(c => c.Visit.ClinicId == 5)
                                  .Select(c => c.VisitId)
                                  .ToList();

// is not the same as

WHERE(dbo.Visit.ClinicId = '5') 
   AND(dbo.Recommendation.Comments = '') OR (dbo.Recommendation.Comments IS NULL)

您首先要指示所有注释或不为null或为空的结果，您的sql语句要求的结果是

如果您要模拟SQL语句，请将linq查询更改为此。

var recommend1 = db.Recommendation.Where(c => c.Comments == "" || c.Comments == null)
                                  .Where(c => c.Visit.ClinicId == 5)
                                  .Select(c => c.VisitId)
                                  .ToList();

Linq查询不会返回与SQL查询相同的数据

1 个答案: