所以我有以下情況：如您所見，某些字段為空，因此我想在插入記錄之前檢查表中是否已經(jīng)存在goal該記錄，我要插入的記錄包含與表中已經(jīng)可用的記錄完全相同的結(jié)構(gòu)。這是我的代碼：public bool CheckGoalExist(Goal goal, Goal.GoalType type, int matchId){    using (MySqlConnection connection = new DBConnection().Connect())    {        using (MySqlCommand command = new MySqlCommand())        {            command.Connection = connection;            command.CommandText = "SELECT COUNT(*) FROM goal " +                "WHERE player_marker_id = @player_marker_id AND " +                "team_id = @team_id AND " +                "player_assist_id = @player_assist_id AND " +                "match_id = @match_id AND " +                    "minute = @minute AND " +                    "type = @type";            command.Parameters.AddWithValue("@team_id", goal.TeamId);            command.Parameters.AddWithValue("@player_marker_id", goal.MarkerPlayer.Id);            command.Parameters.AddWithValue("@player_assist_id", goal.AssistPlayer?.Id);            command.Parameters.AddWithValue("@match_id", matchId);            command.Parameters.AddWithValue("@minute", goal.Minute);            command.Parameters.AddWithValue("@type", GetGoalTypeId(type));            return Convert.ToBoolean(command.ExecuteScalar());        }    }}這將返回，false但值goal是這樣的：TeamId = 95MarkerPlayer.Id = 122AssistPlaer = nullmatchId = 2564940Minute = 82'Type = 5為什么返回false？