The optimization process and recommendations:

1. Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.

Optimal indexes for this query:

ALTER TABLE `deal_master` ADD INDEX `deal_master_idx_swap_lcr_custo_agree_statu_sales` (`swap_commitment`,`lcr_zone`,`customer_interconnect`,`agreement_no`,`status`,`sales_person`);
ALTER TABLE `trans_details_buy` ADD INDEX `trans_buy_idx_cdr_id` (`cdr_id`);
ALTER TABLE `trans_details_sell` ADD INDEX `trans_sell_idx_lcr_zon_sig_net_cdr_id_start` (`lcr_zone`,`sig_netgroup`,`cdr_id`,`start_position`);

The optimized query:

SELECT
        m.agreement_no,
        m.status,
        m.sales_person,
        m.swap_carrier,
        m.swap_commitment,
        m.zone,
        m.lcr_zone,
        m.customer_interconnect,
        SUBSTRING(CAST(m.start_pos AS nvarchar),
        1,
        4) + '-' + SUBSTRING(CAST(m.start_pos AS nvarchar),
        5,
        2) + '-' + SUBSTRING(CAST(m.start_pos AS nvarchar),
        7,
        2) start_date,
        SUBSTRING(CAST(m.end_pos AS nvarchar),
        1,
        4) + '-' + SUBSTRING(CAST(m.end_pos AS nvarchar),
        5,
        2) + '-' + SUBSTRING(CAST(m.end_pos AS nvarchar),
        7,
        2) end_date,
        m.target_minutes,
        m.target_sell_rate,
        m.target_buy_rate,
        m.target_sales,
        m.target_cost,
        m.target_profit,
        SUM(s.quantized_duration) / 60 DG_minute,
        SUM(s.charge) DG_sales,
        SUM(b.charge) DG_cost 
    FROM
        deal_master m,
        trans_details_sell s,
        trans_details_buy b 
    WHERE
        m.lcr_zone = s.lcr_zone 
        AND m.customer_interconnect = s.sig_netgroup 
        AND m.swap_commitment = 'Sell' 
        AND s.cdr_id = b.cdr_id 
        AND s.start_position BETWEEN m.start_pos AND m.end_pos 
    GROUP BY
        m.agreement_no,
        m.status,
        m.sales_person,
        m.swap_carrier,
        m.swap_commitment,
        m.zone,
        m.lcr_zone,
        m.customer_interconnect,
        m.start_pos,
        m.end_pos,
        m.target_minutes,
        m.target_sell_rate,
        m.target_buy_rate,
        m.target_sales,
        m.target_cost,
        m.target_profit 
    ORDER BY
        1