Question

考虑以下查询

SELECT
  FlightDate,
  FlightNum,
  Origin,
  Dest,
  AirlineID
FROM
  ontime1
WHERE 
  FlightDate >= (SELECT MIN(FlightDate) FROM ontime2 WHERE Origin='JFK') AND
  FlightDate <= (SELECT MAX(FlightDate) FROM ontime2 WHERE Origin='JFK') AND
  AirlineID IN (SELECT AirlineID FROM ontime2 WHERE Origin='JFK')
LIMIT 10;

ontime1->根据FlightDate编制索引
ontime2->根据起源，目的地建立索引

由于表数据很大，因此联接表也不是最佳选择

如何在不一次又一次重复相同查询的情况下重用内部查询？

Answer 1

考虑使用WITH Clause：

WITH (
  SELECT (MIN(FlightDate), MAX(FlightDate), groupUniqArray(AirlineID)) /* tuple with required aggregates */
  FROM ontime2
  WHERE Origin='JFK'
) AS cte
SELECT
  FlightDate,
  FlightNum,
  Origin,
  Dest,
  AirlineID
FROM
  ontime1
WHERE 
  FlightDate >= cte.1 AND
  FlightDate <= cte.2 AND
  has(cte.3, AirlineID)
LIMIT 10;

通过仅重复使用一次内部查询来优化查询

1 个答案: