Difference with Parameters.Add and Parameters.AddWithValue

With Add() method you may restrict user input by specifying type and length of data - especially for varchar columns.

.Parameters.Add("@name",SqlDbType.VarChar,30).Value=varName;

In case of AddWithValue() (implicit conversion of value) method, it sends nvarchar value to the database.

I believe there are also some cons to using AddWithValue which affect the SQL Cache Excection Plan, see the Parameter Length section here

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