通过DataReader获取sql查询的字段元数据信息

原理

应用程序调用 GetSchemaTable()↓
ADO.NET 驱动程序生成元数据查询SQL↓
发送到数据库服务器执行↓
数据库返回结果集架构信息（不包含实际数据）↓
ADO.NET 解析架构信息并构建 DataTable↓
返回包含完整列信息的 DataTable

sqlsugar

            var sql = $@"select * from sys_database d
left join sys_table t
on d.""id"" = t.database_id";//var behavior80c9dce3fe3b43b8847e55614ab45b56 = CommandBehavior.SequentialAccess |  CommandBehavior.CloseConnection;var behavior80c9dce3fe3b43b8847e55614ab45b56 = CommandBehavior.SchemaOnly;res = new List<object>();var result = await sqlSugar.Ado.GetCommand(sql, paraList.ToArray()).ExecuteReaderAsync(CommandBehavior.SchemaOnly);var schema = result.GetSchemaTable();foreach (DataRow row in schema.Rows){string columnName = row["ColumnName"].ToString();Type dataType = (Type)row["DataType"];int columnSize = (int)row["ColumnSize"];//bool isNullable = (bool)row["AllowDBNull"];var isNullable = row["AllowDBNull"];// 还有其他信息，如精度、小数位数等Console.WriteLine($"列名: {columnName}, 类型: {dataType}, 大小: {columnSize}, 可空: {isNullable}");}

ado

using (SqlCommand command = new SqlCommand("SELECT TOP 0 * FROM employees", connection))
{using (SqlDataReader reader = command.ExecuteReader()){// 获取数据表的Schemavar schemaTable = reader.GetSchemaTable();// 遍历每一列的Schema信息foreach (DataRow row in schemaTable.Rows){string columnName = (string)row["ColumnName"];Type dataType = (Type)row["DataType"];int maxLength = (int)row["ColumnSize"];bool allowNull = (bool)row["AllowDBNull"];// 输出列的信息Console.WriteLine("列名：{columnName}");Console.WriteLine("数据类型：{dataType}");Console.WriteLine("最大长度：{maxLength}");Console.WriteLine("是否允许为空：{allowNull}");Console.WriteLine("---------------------------------------");}}
}