如何使用DISTINCT ON和JOIN MULTY values优化SQL查询？

Question

我有一个这样的查询，其中join~6000个值

SELECT DISTINCT ON(user_id)
                user_id,
                finished_at as last_deposit_date,
                CASE When currency = 'RUB' Then amount_cents  END as last_deposit_amount_cents
            FROM    payments
            JOIN (VALUES (5),(22),(26)) --~6000 values
            AS v(user_id) USING (user_id)
            WHERE action = 'deposit' 
                AND success = 't'
                AND currency IN ('RUB')
            ORDER BY user_id, finished_at DESC

多值查询的查询计划：

Unique  (cost=444606.97..449760.44 rows=19276 width=24) (actual time=6129.403..6418.317 rows=5991 loops=1)
  Buffers: shared hit=2386527, temp read=7807 written=7808
  ->  Sort  (cost=444606.97..447183.71 rows=1030695 width=24) (actual time=6129.401..6295.457 rows=1877039 loops=1)
        Sort Key: payments.user_id, payments.finished_at DESC
        Sort Method: external merge  Disk: 62456kB
        Buffers: shared hit=2386527, temp read=7807 written=7808
        ->  Nested Loop  (cost=0.43..341665.35 rows=1030695 width=24) (actual time=0.612..5085.376 rows=1877039 loops=1)
              Buffers: shared hit=2386521
              ->  Values Scan on "*VALUES*"  (cost=0.00..75.00 rows=6000 width=4) (actual time=0.002..4.507 rows=6000 loops=1)
              ->  Index Scan using index_payments_on_user_id on payments  (cost=0.43..54.78 rows=172 width=28) (actual time=0.010..0.793 rows=313 loops=6000)
                    Index Cond: (user_id = "*VALUES*".column1)
                    Filter: (success AND ((action)::text = 'deposit'::text) AND ((currency)::text = 'RUB'::text))
                    Rows Removed by Filter: 85
                    Buffers: shared hit=2386521
Planning time: 5.886 ms
Execution time: 6429.685 ms

我使用PosgreSQL 10.8.0。有没有可能加快这个查询的速度？

我尝试用递归替换DISTINCT：

WITH RECURSIVE t AS (
 (SELECT min(user_id) AS user_id FROM payments)
 UNION ALL
 SELECT (SELECT min(user_id) FROM payments  
 WHERE user_id > t.user_id      
 ) AS user_id FROM
t   
  WHERE t.user_id IS NOT NULL
 )
SELECT payments.* FROM t
JOIN (VALUES (5),(22),(26)) --~6000 VALUES
AS v(user_id) USING (user_id)
, LATERAL (
 SELECT user_id,
        finished_at as last_deposit_date,
        CASE When currency = 'RUB' Then amount_cents  END as last_deposit_amount_cents FROM payments            
        WHERE payments.user_id=t.user_id
            AND action = 'deposit' 
        AND success = 't'
        AND currency IN ('RUB')     
        ORDER BY finished_at DESC LIMIT 1
) AS payments

WHERE t.user_id IS NOT NULL;

但结果更慢。

哈希连接（成本=418.67..21807.22行=3000宽度=24）（实际时间=16.804..10843.174行=5991循环=1）哈希Cond：（t.user_id="VALUES"。专栏1）缓冲区：共享命中=6396763 CTE t-

Answer 1

对于此查询：

SELECT DISTINCT ON (user_id)
       p.user_id,
       p.finished_at as last_deposit_date,
       (CASE WHEN p.currency = 'RUB' THEN p.amount_cents  END) as last_deposit_amount_cents
FROM payments p JOIN
     (VALUES (5),( 22), (26) --~6000 values
     ) v(user_id)
     USING (user_id)
WHERE p.action = 'deposit' AND
      p.success = 't' ND
      p.currency = 'RUB'
ORDER BY p.user_id, p.finished_at DESC;

我不完全理解CASE表达式，因为WHERE正在过滤掉所有其他值。

这就是说，我希望（操作、成功、货币、用户id、在desc完成）的索引会有所帮助。