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sql - 优化以下 postgreSQL 代码的可能方法是什么？

问题描述

我编写了这个 SQL 查询来从 greenplum datalake 中获取数据。主表有 800,000 行，我正在与其他表连接。下面的查询花费了大量的时间来给出结果。查询时间较长的可能原因是什么？如何解决？

select    
          a.pole,
          t.country_name,
          a.service_area,  
          a.park_name,

          t.turbine_platform_name,
          a.turbine_subtype,
          a.pad as "turbine_name",
          t.system_number as "turbine_id",
          a.customer,
          a.service_contract,   

          a.component,
          c.vendor_mfg as "component_manufacturer",

          a.case_number,
          a.description as "case_description",
          a.rmd_diagnosis as "case_rmd_diagnostic_description",
          a.priority as "case_priority",
          a.status as "case_status",
          a.actual_rootcause as "case_actual_rootcause",
          a.site_trends_feedback as "case_site_feedback",
          a.added as "date_case_added",
          a.start as "date_case_started",
          a.last_flagged as "date_case_flagged_by_algorithm_latest",
          a.communicated as "date_case_communicated_to_field",
          a.field_visible_date as "date_case_field_visbile_date",
          a.fixed as "date_anamoly_fixed",
          a.expected_clse as "date_expected_closure",
          a.request_closure_date as "date_case_request_closure",
          a.validation_date as "date_case_closure",
          a.production_related,
          a.estimated_value as "estimated_cost_avoidance",
          a.cms,
          a.anomaly_category,
          a.additional_information as "case_additional_information",
          a.model,
          a.full_model,
          a.sent_to_field as "case_sent_to_field"

      from app_pul.anomaly_stage a
 left join ge_cfg.turbine_detail t on a.scada_number = t.system_number and a.added > '2017-12-31'
 left join tbwgr_v.pmt_wmf_tur_component_master_t c on a.component = c.component_name

标签： sqlpostgresqlquery-optimizationgreenplum

解决方案

您的查询基本上是：

 select . . .
 from app_pul.anomaly_stage a left join
      ge_cfg.turbine_detail t 
      on a.scada_number = t.system_number and
         a.added > '2017-12-31' left join
         tbwgr_v.pmt_wmf_tur_component_master_t c
         on a.component = c.component_name

首先，条件 ona被忽略，因为它是left joinandon子句中的第一个表。因此，我假设您实际上打算对其进行过滤，因此将查询编写为：

 select . . .
 from app_pul.anomaly_stage a left join
      ge_cfg.turbine_detail t 
      on a.scada_number = t.system_number left join
      tbwgr_v.pmt_wmf_tur_component_master_t c
      on a.component = c.component_name
 where a.added > '2017-12-31'

这可能有助于提高性能。然后在 Postgres 中，您需要在turbine_detail(system_number)和上建立索引pmt_wmf_tur_component_master_t(component_name)。索引是否对第一个表有帮助是值得怀疑的，因为您已经在选择大量数据。

我不确定索引在 Greenplum 中是否合适。

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