以下是测试中的数据集和表的几种方法：

Dataset ds;

if (ds != null) {}  //Check if Dataset is null.

if (ds.Tables.Count > 0) {}  //Check if Dataset has any tables.

if (ds.Tables.Contains("tableName")) {}  //Check if Dataset has a specific table name.

Datatable dt = ds.Tables["tableName"];  //Get the specific table.
if (dt.Rows.Count > 0) {}  //Check if specific table has rows.

if (dt.Columns.Contains("columnName")) {}  //Check if specific table has a specific column name.