postgreSQL - 查詢結果不正確

Question

我有以下兩個查詢：

Return the number of flights for each manufacturer:

SELECT COUNT(flight) AS num_flights, manufacturer
FROM flights, planes
WHERE flights.tailnum = planes.tailnum
GROUP BY manufacturer
ORDER BY num_flights DESC

返回（此處並非所有結果都可見，總共 27 行）：

-------------+---------------------------------+--+--+--+
| num_flights | manufacturer                    |  |  |  |
+-------------+---------------------------------+--+--+--+
| 67623       | "BOEING"                        |  |  |  |
+-------------+---------------------------------+--+--+--+
| 36244       | "AIRBUS INDUSTRIE"              |  |  |  |
+-------------+---------------------------------+--+--+--+
| 11676       | "AIRBUS"                        |  |  |  |
+-------------+---------------------------------+--+--+--+
| 8932        | "MCDONNELL DOUGLAS AIRCRAFT CO" |  |  |  |
+-------------+---------------------------------+--+--+--+
| 4856        | "EMBRAER"                       |  |  |  |
+-------------+---------------------------------+--+--+--+
| 3998        | "MCDONNELL DOUGLAS"             |  |  |  |
+-------------+---------------------------------+--+--+--+
| 1259        | "MCDONNELL DOUGLAS CORPORATION" |  |  |  |
+-------------+---------------------------------+--+--+--+
| 247         | "CESSNA"                        |  |  |  |
+-------------+---------------------------------+--+--+--+
| 162         | "PIPER"                         |  |  |  |
+-------------+---------------------------------+--+--+--+
| 65          | "BELL"                          |  |  |  |
+-------------+---------------------------------+--+--+--+
| 63          | "DEHAVILLAND"                   |  |  |  |
+-------------+---------------------------------+--+--+--+
| 63          | "FRIEDEMANN JON"                |  |  |  |
+-------------+---------------------------------+--+--+--+
| 55          | "STEWART MACO"                  |  |  |  |
+-------------+---------------------------------+--+--+--+
| 54          | "LAMBERT RICHARD"               |  |  |  |
+-------------+---------------------------------+--+--+--+
| 51          | "KILDALL GARY"                  |  |  |  |
+-------------+---------------------------------+--+--+--+
| 47          | "BEECH"                         |  |  |  |
+-------------+---------------------------------+--+--+--+
| 44          | "MARZ BARRY"                    |  |  |  |
+-------------+---------------------------------+--+--+--+
| 42          | "AMERICAN AIRCRAFT INC"         |  |  |  |
+-------------+---------------------------------+--+--+--+
| 40          | "LEBLANC GLENN T"               |  |  |  |
+-------------+---------------------------------+--+--+--+
| 32          | "AGUSTA SPA"                    |  |  |  |
+-------------+---------------------------------+--+--+--+
| 27          | "SIKORSKY"                      |  |  |  |
+-------------+---------------------------------+--+--+--+
| 25          | "PAIR MIKE E"                   |  |  |  |
+-------------+---------------------------------+--+--+--+
| 22          | "DOUGLAS"                       |  |  |  |
+-------------+---------------------------------+--+--+--+
| 19          | "LEARJET INC"                   |  |  |  |
+-------------+---------------------------------+--+--+--+
| 18          | "AVIAT AIRCRAFT INC"            |  |  |  |
+-------------+---------------------------------+--+--+--+
| 17          | "HURLEY JAMES LARRY"            |  |  |  |
+-------------+---------------------------------+--+--+--+
| 13          | "GULFSTREAM AEROSPACE"          |  |  |  |
+-------------+---------------------------------+--+--+--+

還有一個：

Return manufacturers with more than 200 planes:

SELECT COUNT(tailnum) AS num_planes, manufacturer 
FROM planes 
GROUP BY manufacturer 
HAVING COUNT(*) > 200 
ORDER BY num_planes DESC

返回：

+------------+--------------------+
| num_planes | manufacturer       |
+------------+--------------------+
| 1630       | "BOEING"           |
+------------+--------------------+
| 400        | "AIRBUS INDUSTRIE" |
+------------+--------------------+
| 368        | "BOMBARDIER INC"   |
+------------+--------------------+
| 336        | "AIRBUS"           |
+------------+--------------------+
| 299        | "EMBRAER"          |
+------------+--------------------+

現在我正在嘗試查詢擁有超過 200 架飛機的每個制造商的航班數量。

編寫了以下查詢：

SELECT COUNT(flight) AS num_flights, pl.manufacturer
FROM flights fl, planes pl JOIN
(SELECT COUNT(tailnum) AS num_planes, pl2.manufacturer
    FROM planes pl2
    GROUP BY pl2.manufacturer 
    HAVING COUNT(*) > 200
    ORDER BY num_planes DESC) tm
    ON pl.manufacturer = tm.manufacturer
GROUP BY pl.manufacturer
ORDER BY num_flights DESC

但是，此查詢返回的航班數量不正確，並且需要很長時間才能執行：

+-------------+--------------------+
| num_flights | manufacturer       |
+-------------+--------------------+
| 262029020   | "BOEING"           |
+-------------+--------------------+
| 64301600    | "AIRBUS INDUSTRIE" |
+-------------+--------------------+
| 59157472    | "BOMBARDIER INC"   |
+-------------+--------------------+
| 54013344    | "AIRBUS"           |
+-------------+--------------------+
| 48065446    | "EMBRAER"          |
+-------------+--------------------+

我在這里做錯了什么？

表結構：

planes:

CREATE TABLE planes
(
     tailnum VARCHAR(6),
     manufacturer VARCHAR(50)
)

+----------+--------------------+
| tailnum  | manufacturer       |
+----------+--------------------+
| "N10156" | "EMBRAER"          |
+----------+--------------------+
| "N102UW" | "AIRBUS INDUSTRIE" |
+----------+--------------------+
| "N103US" | "AIRBUS INDUSTRIE" |
+----------+--------------------+
| "N104UW" | "AIRBUS INDUSTRIE" |
+----------+--------------------+
| "N10575" | "EMBRAER"          |
+----------+--------------------+
| "N105UW" | "AIRBUS INDUSTRIE" |
+----------+--------------------+
| "N107US" | "AIRBUS INDUSTRIE" |
+----------+--------------------+
| ...      | ...                |
+----------+--------------------+

flights:

CREATE TABLE flights
(
     flight INT,
     tailnum VARCHAR(6)
)

+--------+----------+
| flight | tailnum  |
+--------+----------+
| 1545   | "N14228" |
+--------+----------+
| 1714   | "N24211" |
+--------+----------+
| 1141   | "N619AA" |
+--------+----------+
| 461    | "N668DN" |
+--------+----------+
| 1696   | "N39463" |
+--------+----------+
| ...    | ...      |
+--------+----------+

Answer 1

您可以試試這個（通過 tailnum 加入飛機和航班），計算 tailnums 和按制造商分組的航班，並通過在COUNT(tailnum)上的子句進行過濾。

    SELECT manufacturer AS "Manufacturer", 
           COUNT(DISTINCT tailnum) AS "Number of planes",
           COUNT(flights) as "Number of flights",
      FROM planes
INNER JOIN flights
        ON (planes.tailnum=flights.tailnum)
  GROUP BY manufacturer
    HAVING COUNT(DISTINCT tailnum)>200
  ORDER BY 3