/// <summary>
/// 查询返回第一行第一列字段的值
/// </summary>
/// <typeparam name="TResult">接受查询结果类型</typeparam>
/// <param name="field">查询的字段</param>
/// <returns></returns>
public TResult ToScalar <TResult>(string field)
{
if (!string.IsNullOrEmpty(GroupByText))
{
throw new ArgumentException("聚合查询不允许使用 GROUP BY 条件！");
}
Fields.Clear();
Fields.Add(field);
string cmdText = ToSQL();
SQLExecute execute = byMaster ? dbContext.ByMaster().Execute : dbContext.Execute;
object result = execute.ExecuteScalar(CommandType.Text, cmdText, Parameters.ToArray());
return(result == null ? default : (TResult)result);
}
