C#如何获取Oracle数据库中的所有数据

Question

我在 Oracle 11g 中有 21 个表，我需要使用 JOIN 子句来显示它们。但是查询太慢了，抛出了System.OutOfMemoryException

我当前的代码：

   try
        {
            //string ConString;
            using (OracleConnection con = new OracleConnection(ConString))
            {
                //string query = "SELECT PAX.CREATION_DATE,PAX.PNR,PAX.PAX_NMBR,PAX.UPDATE_LEVEL_MOD,PAX.PAX_NAME,PAX.CHANGE_OR_CANCEL_IND,PAX_SEATS.LEG_NMBR,PAX_SEATS.INSTANCE_NMBR,pax_seats.ssr_cd,pax_seats.carrier_cd,pax_seats.seat_nmbr,pax_seats.previous_status_codes FROM PAX INNER JOIN PAX_SEATS ON PAX.PNR = PAX_SEATS.PNR";
                string query1 = "SELECT PNR FROM HISTORY_LEGS";
                string query2 = "SELECT PAX.CREATION_DATE,PAX.PNR,PAX.PAX_NMBR,PAX.UPDATE_LEVEL_MOD,PAX.PAX_NAME,PAX.CHANGE_OR_CANCEL_IND,PAX_SEATS.LEG_NMBR,PAX_SEATS.INSTANCE_NMBR,pax_seats.ssr_cd,pax_seats.carrier_cd,pax_seats.seat_nmbr,pax_seats.previous_status_codes,PAX_SSRS.SSR_NMBR,PAX_TKT.TKTNMBR,PAX_TKT.ISSUING_AIRLINE, PAX_TKT.ISSUING_OFFC_NMBR, PAX_TKT.ISSUING_COUNTER_CD, PAX_TKT.ISSUING_AGNT_NMBR, PAX_TKT.TKT_IND, PAX_TKT.TKT_STATUS, PAX_TKT.TARIFICATION_IND,PAX_TKT.S_IND,PAX_TKT.ISSUANCE_DATE FROM PAX INNER JOIN PAX_SEATS ON PAX.PNR = PAX_SEATS.PNR RIGHT JOIN PAX_SSRS ON PAX.PNR = PAX_SSRS.PNR RIGHT JOIN PAX_TKT ON PAX.PNR = PAX_TKT.PNR";
                //string query4 = "SELECT * FROM PAX";
                //string query3 = "SELECT PAX.PAX_NMBR,PAX.PAX_NAME,RES_LEGS.ARNK_IND,RES_LEGS.CARRIER_CD1,RES_LEGS.CARRIER_CD2,RES_LEGS.FLT_NMBR,RES_LEGS.CLASS_CD,RES_LEGS.DAY_OF_WEEK,RES_LEGS.FLT_DATE,RES_LEGS.LEG_ORIGIN_CD,RES_LEGS.LEG_DES_CD,RES_LEGS.CURRENT_STATUS_CD,RES_LEGS.NUMBER_IN_PARTY,RES_LEGS.DP_TIME,RES_LEGS.AR_TIME,RES_LEGS.DATE_CHANGE_IND,RES_LEGS.FLT_IRREGULARITY_IND,RES_LEGS.LEG_TXT,RES_LEGS.PREVIOUS_STATUS_CODES,RES_LEGS.MESSAGE FROM RES_LEGS INNER JOIN PAX ON RES_LEGS.PNR = PAX.PNR";
                OracleCommand cmd = new OracleCommand(query2, con);
                OracleDataAdapter oda = new OracleDataAdapter(cmd);
                DataSet ds = new DataSet();
                oda.Fill(ds);
                //dataGridView1.RowHeadersWidthSizeMode = DataGridViewRowHeadersWidthSizeMode.EnableResizing;
                //dataGridView1.RowHeadersVisible = false;
                if (ds.Tables.Count > 0)
                {
                    dataGridView1.DataSource = ds.Tables[0].DefaultView;
                }

            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }

问题：

1. 如何获取所有数据？
2. 如何防止 System.OutofMemory？
3. 如何提高查询执行性能？

Answer 1

您可以查看关键字段上的索引以加快查询速度，但如果您返回很多行，您将在某处遇到一些内存上限。

如果可以的话，我建议实现一些分页：Paging with Oracle。

这将让您恢复较小的数据块，使其更快且不太可能达到任何内存限制。