c# - How to pass sqlparameter to IN()?

Question

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Answer 1

You have to create one parameter for each value that you want in the IN clause.

The SQL needs to look like this:

SELECT userId, username 
FROM Users 
WHERE userId IN (@UserId1, @UserId2, @UserId3, ...) 

So you need to create the parameters and the IN clause in the foreach loop.
Something like this (out of my head, untested):

StringBuilder sb = new StringBuilder();
int i = 1;

foreach (User user in UserList)
{
    // IN clause
    sb.Append("@UserId" + i.ToString() + ",");

    // parameter
    YourCommand.Parameters.AddWithValue("@UserId" + i.ToString(), user.UserId);

    i++;
}