Question

如何改善查询？

WITH womenRating AS ( SELECT count(train_type) as trainCount, train_type FROM trainRoutine
INNER JOIN client ON client.id = trainRoutine.client_id
WHERE client.gender = 'Woman'
GROUP BY train_type
ORDER BY trainCount DESC ),
     menRating AS (
SELECT count(train_type) as trainCount, train_type FROM trainRoutine
INNER JOIN client ON client.id = trainRoutine.client_id
WHERE client.gender = 'Man'
GROUP BY train_type
ORDER BY trainCount DESC )
     select a.train_type, DENSE_RANK() OVER (ORDER BY a.traincount DESC) as women, DENSE_RANK() OVER (ORDER BY b.traincount DESC) as men
FROM womenRating a
FULL OUTER JOIN menRating b ON a.train_type = b.train_type;

由于

而出现问题

FULL OUTER JOIN menRating b ON a.train_type = b.train_type

如果左表“womenRating”没有第二个表所具有的train_type值，则会有一个空字段，而我的DENSE_RANK（）会将该行计为№1

Answer 1

使用条件聚合：

SELECT train_type,
       sum( (c.gender = 'Woman')::int) as women_count,
       sum( (c.gender = 'Man')::int) as men_count,
       dense_rank() over (order by sum( (c.gender = 'Woman')::int) desc) as women_rank,
       dense_rank() over (order by sum( (c.gender = 'Man')::int) desc) as men_rank
FROM trainRoutine tr INNER JOIN
     client c
     ON c.id = tr.client_id
GROUP BY train_type
ORDER BY trainCount DESC

PostgreSQL的。改善查询。 WITH

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