Question

提前感谢那些会帮助我的人。我必须优化这个PostgreSQL查询，创建一些索引。

SELECT D.market, D.symbol, D.company_name, D.first_date, D.last_date, D.days
FROM (SELECT MIN(B.DIFF) AS MIN_DIFF 
      FROM (SELECT A.market AS market, A.symbol AS symbol, A.company_name AS company_name, MIN(A.date) AS first_date, MAX(A.date) AS last_date, MAX(A.date) - MIN(A.date) AS DIFF
            FROM (SELECT m.market AS market, s.company_name AS company_name, p.symbol AS symbol, p.date AS date 
                  FROM market m JOIN stock_symbols s ON (s.market = m.market) JOIN stock_price p ON (s.symbol = p.symbol)) AS A
                  GROUP BY A.market, A.symbol, A.company_name) AS B) AS C JOIN (SELECT C.market AS market, C.symbol AS symbol, C.company_name AS company_name, MIN(C.date) AS first_date, MAX(C.date) AS last_date, MAX(C.date) - MIN(C.date) AS days
                                                                                FROM (SELECT m.market AS market, s.company_name AS company_name, p.symbol AS symbol, p.date AS date 
                                                                                      FROM market m JOIN stock_symbols s ON (s.market = m.market) JOIN stock_price p ON (s.symbol = p.symbol)) AS C
                                                                                      GROUP BY C.market, C.symbol, C.company_name) AS D ON (D.days = C.MIN_DIFF)

我尝试在散列连接条件（s.market = m.market）和（s.symbol = p.symbol）上创建索引，但DBMS不接受它们。执行时，我得到以下实际执行计划成本：

"Hash Join  (cost=28626.01..31951.32 rows=359 width=66)"
"  Hash Cond: (((max(p.date) - min(p.date))) = (min(((max(p_1.date) - mi(p_1.date))))))"
"  ->  GroupAggregate  (cost=12697.02..15031.20 rows=71821 width=58)"
"        Group Key: m.market, p.symbol, s.company_name"
"        ->  Sort  (cost=12697.02..12876.57 rows=71821 width=58)"
"              Sort Key: m.market, p.symbol, s.company_name"
"              ->  Hash Join  (cost=150.12..4201.89 rows=71821 width=58)"
"                    Hash Cond: (p.symbol = s.symbol)"
"                    ->  Seq Scan on stock_price p  (cost=0.00..2588.04 rows=149104 width=8)"
"                    ->  Hash  (cost=121.85..121.85 rows=2262 width=54)"
"                          ->  Hash Join  (cost=1.02..121.85 rows=2262 width=54)"
"                                Hash Cond: ((s.market)::text = (m.market)::text)"
"                                ->  Seq Scan on stock_symbols s  (cost=0.00..81.24 rows=4524 width=32)"
"                                ->  Hash  (cost=1.01..1.01 rows=1 width=28)"
"                                      ->  Seq Scan on market m  (cost=0.00..1.01 rows=1 width=28)"
"  ->  Hash  (cost=15928.98..15928.98 rows=1 width=4)"
"        ->  Aggregate  (cost=15928.96..15928.97 rows=1 width=4)"
"              ->  GroupAggregate  (cost=12697.02..15031.20 rows=71821 width=58)"
"                    Group Key: m_1.market, p_1.symbol, s_1.company_name"
"                    ->  Sort  (cost=12697.02..12876.57 rows=71821 width=58)"
"                          Sort Key: m_1.market, p_1.symbol, s_1.company_name"
"                          ->  Hash Join  (cost=150.12..4201.89 rows=71821 width=58)"
"                                Hash Cond: (p_1.symbol = s_1.symbol)"
"                                ->  Seq Scan on stock_price p_1  (cost=0.00..2588.04 rows=149104 width=8)"
"                                ->  Hash  (cost=121.85..121.85 rows=2262 width=54)"
"                                      ->  Hash Join  (cost=1.02..121.85 rows=2262 width=54)"
"                                            Hash Cond: ((s_1.market)::text = (m_1.market)::text)"
"                                            ->  Seq Scan on stock_symbols s_1  (cost=0.00..81.24 rows=4524 width=32)"
"                                            ->  Hash  (cost=1.01..1.01 rows=1 width=28)"
"                                                  ->  Seq Scan on market m_1  (cost=0.00..1.01 rows=1 width=28)"

有人能帮帮我吗？非常感谢!!!!

使用join，group by优化PostgreSQL查询

0 个答案: