c# - If 和 Null sql 语句

Question

更新:这个说法是否正确

  public void CheckReputationIfNull()
{
    StringBuilder sb = new StringBuilder();
    sb.Append("DECLARE @isReputationNull int");
    sb.Append(" SET @isReputationNull=( SELECT Reputation");
    sb.Append(" FROM Users u");
    sb.Append(" INNER JOIN Comments c ON c.UsersID = u.UsersID");
    sb.Append(" WHERE c.CommentsID = @CommentsID)");

sb.Append(" BEGIN IF ( @isReputationNull IS NULL)");
sb.Append("UPDATE u ");
sb.Append(" SET Reputation = 0");
sb.Append(" FROM Users u");
sb.Append(" END");

using (SqlConnection conn = new SqlConnection(AllQuestionsPresented.connectionString))
{
    SqlCommand cmd = new SqlCommand(sb.ToString(), conn);
    cmd.Parameters.Add("@CommentsID", SqlDbType.Int).Value = commentID;
    conn.Open();
    cmd.ExecuteNonQuery();
}

Answer 1

ISNULL 是一个函数，所以你可以这样做:

ISNULL(MyColumn, 'alternative value')

你要做的是:

IF (MyColumn IS NULL)

检查列是否为 NULL。