PostgreSQL优化查询

Question

我想优化此查询：

WITH t AS (
        SELECT c.pl_number, c.def
        FROM rac_import i JOIN (
            SELECT
                t.pl_number,
                (CASE WHEN t.self_bk_lists_id IS NOT NULL THEN 1 
                WHEN t.ad_hoc_parcels_id IS NOT NULL AND t.service IN('105', '138', '107', '139') THEN 2
                ELSE 3 END) AS def
            FROM dblink('hostaddr=x.x.x.x port=xxx dbname=xxxx user=xxxx password=xxxx'::text, '
            SELECT tr.pl_number, tr.self_bk_lists_id, tr.ad_hoc_parcels_id, s.service 
            FROM cashmodul.transmission_register tr
            LEFT OUTER JOIN scans.scandata05 s ON tr.pl_number = s.parcelno'::text)
            t(pl_number character varying(14), self_bk_lists_id integer, ad_hoc_parcels_id integer, service character varying)
        ) AS c ON i.parcelno = c.pl_number
        WHERE i.akcija = 3
    )
    UPDATE rac_import
    SET def = t.def
    FROM t
    WHERE parcelno = t.pl_number

当前执行时间大约是4-5秒，我希望大约0.5秒。

编辑：

UPDATE rac_import AS i SET def = (CASE WHEN t.self_bk_lists_id IS NOT NULL THEN 1 
    WHEN t.ad_hoc_parcels_id IS NOT NULL AND t.service IN('105', '138', '107', '139') THEN 2
    ELSE 3 END)
        FROM (
            SELECT
                t.pl_number,
                t.self_bk_lists_id,
                t.ad_hoc_parcels_id,
                t.service
            FROM dblink('hostaddr=x.x.x.x port=xxxx dbname=xxxx user=xxxx password=xxxx'::text, '
            SELECT tr.pl_number, tr.self_bk_lists_id, tr.ad_hoc_parcels_id, s.service 
            FROM cashmodul.transmission_register tr
            LEFT OUTER JOIN scans.scandata05 s ON tr.pl_number = s.parcelno'::text)
            t(pl_number character varying(14), self_bk_lists_id integer, ad_hoc_parcels_id integer, service character varying)
        ) AS t
        WHERE i.parcelno = t.pl_number AND i.akcija = 3

使用此代码管理减少1秒。