Oracle：打开声明的游标会花费太多时间。如何优化呢？

Question

我有一个函数，并且在此函数中声明了我的光标。功能运行非常慢（大约14秒）。我认为这是因为它确实很复杂。我决定在探查器中测试我的功能。令我震惊的是，它花了90％的时间处理与光标相关的事情。 4秒钟检查光标是否为空，9秒钟打开FOR LOOP的光标。结果如下：

我该如何减少这些事情所需的时间？

这是我的光标。它通常仅包含1-6行。并且此查询在瞬间返回行。

FUNCTION finder (...) RETURN NUMBER IS 
        ...
CURSOR near_clinics IS   
SELECT a.id, a.full_address, me.answer, me.name, a.nlat, a.nlong, me.in_partner, a.city
          FROM   user.table1 a,
                 (SELECT pnradius AS radius, 111.045 AS distance_unit, 57.2957795 AS rad2deg, 0.01745329251994 AS deg2rad
                  FROM   dual) geo,
                 user.table2 me
          WHERE  a.nlat BETWEEN pnlatitude - (geo.radius / geo.distance_unit) AND
                 pnlatitude + (geo.radius / geo.distance_unit)
          AND    a.nlong BETWEEN pnlongitude - (geo.radius / (geo.distance_unit * cos(deg2rad * (pnlatitude)))) AND
                 pnlongitude + (geo.radius / (geo.distance_unit * cos(deg2rad * (pnlatitude))))
          AND    geo.distance_unit * rad2deg *
                 (acos(cos(deg2rad * (pnlatitude)) * cos(deg2rad * (a.nlat)) * cos(deg2rad * (pnlongitude - a.nlong)) +
                        sin(deg2rad * (pnlatitude)) * sin(deg2rad * (a.nlat)))) < pnradius
          AND    a.parent_id = me.answer
          AND    a.parent_table = 'user.table2';
        ...
    BEGIN
    ...
    END.