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  • 简单改写SQL达到优化目的

    select *
    from (select t.row_id,
    t.supplier_name,
    t.tel,
    address,
    t.contact,
    t.contact_post,
    t.contact_mobi,
    t.contact_tel,
    case
    when project_supp_type = 0 then
    to_number(nvl(t.discount_rate, 0))
    when project_supp_type2 = 0 then
    to_number(nvl(t.discount_rate2, 0))
    when project_supp_type3 = 0 then
    to_number(nvl(t.discount_rate3, 0))
    when project_supp_type4 = 0 then
    to_number(nvl(t.discount_rate4, 0))
    when project_supp_type5 = 0 then
    to_number(nvl(t.discount_rate5, 0))
    when project_supp_type6 = 0 then
    to_number(nvl(t.discount_rate6, 0))
    end as rate
    from md_supplier t
    where t.supplier_type = 4
    and (project_supp_type = 0 or project_supp_type2 = 0 or
    project_supp_type3 = 0 or project_supp_type4 = 0 or
    project_supp_type5 = 0 or project_supp_type6 = 0)
    and t.status = 1
    and exists (select *
    from md_project mp, md_project_supplier mps
    where mp.row_id = mps.project_id
    and mp.status = 1
    
    and supplier_id = t.row_id)
    order by rate desc, t.supplier_name)
    where rownum <= 5
    View Code

     这是原始sql,sql运行4秒出结果,网友反映比较慢

    看了执行计划

    执行计划没有问题,驱动表全表扫描也只是返回27条,无伤大雅,被驱动表view VW_SQ_1

    被驱动表内走了 merge jion,merge jion比nl要强一下,进行全表扫描之后再排序,之后再连接

    问题要看exists中的表 返回227行,在view中 exists中的表有相当于一个驱动表了,他要驱动id 10,每次查询都要全表 ,还要227次,就慢了,就需要改写

    将它提取出来,不让他扫描多次,这就是思路

    改写之后的sql

    with ttt as (select *
                        from md_project mp, md_project_supplier mps
                       where mp.row_id = mps.project_id
                         and mp.status = 1                     
    )
    select *
        from (select t.row_id,
                     t.supplier_name,
                     t.tel,
                     address,
                     t.contact,
                     t.contact_post,
                     t.contact_mobi,
                     t.contact_tel,
                     case
                       when project_supp_type = 0 then
                        to_number(nvl(t.discount_rate, 0))
                       when project_supp_type2 = 0 then
                        to_number(nvl(t.discount_rate2, 0))
                       when project_supp_type3 = 0 then
                        to_number(nvl(t.discount_rate3, 0))
                       when project_supp_type4 = 0 then
                        to_number(nvl(t.discount_rate4, 0))
                       when project_supp_type5 = 0 then
                        to_number(nvl(t.discount_rate5, 0))
                       when project_supp_type6 = 0 then
                        to_number(nvl(t.discount_rate6, 0))
                     end as rate
                from md_supplier t
               where t.supplier_type = 4
                 and (project_supp_type = 0 or project_supp_type2 = 0 or
                     project_supp_type3 = 0 or project_supp_type4 = 0 or
                     project_supp_type5 = 0 or project_supp_type6 = 0)
                 and t.status = 1
                 and exists (select * from ttt where supplier_id = t.row_id)
               order by rate desc, t.supplier_name)
       where rownum <= 5
    View Code

     

    sql运行时间为0.03秒

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  • 原文地址:https://www.cnblogs.com/SUN-PH/p/4766022.html
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