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История изменений

Исправление AlexKiriukha, (текущая версия) : 

explain SELECT     
        product_name,
        type_name
FROM 
        products p, 
        product_types pt
WHERE 
        p.type_id = pt.id;
                                   QUERY PLAN                                    
---------------------------------------------------------------------------------
 Hash Join  (cost=38.58..63.74 rows=1200 width=64)
   Hash Cond: (p.type_id = pt.id)
   ->  Seq Scan on products p  (cost=0.00..22.00 rows=1200 width=36)
   ->  Hash  (cost=22.70..22.70 rows=1270 width=36)
         ->  Seq Scan on product_types pt  (cost=0.00..22.70 rows=1270 width=36)
(5 rows)

=# explain 
SELECT 
        product_name,
        type_name
FROM 
        products p 
                JOIN product_types pt ON p.type_id = pt.id;
                                   QUERY PLAN                                    
---------------------------------------------------------------------------------
 Hash Join  (cost=38.58..63.74 rows=1200 width=64)
   Hash Cond: (p.type_id = pt.id)
   ->  Seq Scan on products p  (cost=0.00..22.00 rows=1200 width=36)
   ->  Hash  (cost=22.70..22.70 rows=1270 width=36)
         ->  Seq Scan on product_types pt  (cost=0.00..22.70 rows=1270 width=36)

не нашел отличий в планах.

Исправление AlexKiriukha, : 

explain SELECT     
        product_name,
        type_name
FROM 
        products p, 
        product_types pt
WHERE 
        p.type_id = pt.id;
                                   QUERY PLAN                                    
---------------------------------------------------------------------------------
 Hash Join  (cost=38.58..63.74 rows=1200 width=64)
   Hash Cond: (p.type_id = pt.id)
   ->  Seq Scan on products p  (cost=0.00..22.00 rows=1200 width=36)
   ->  Hash  (cost=22.70..22.70 rows=1270 width=36)
         ->  Seq Scan on product_types pt  (cost=0.00..22.70 rows=1270 width=36)
(5 rows)

=# explain 
SELECT 
        product_name,
        type_name
FROM 
        products p 
                JOIN product_types pt ON p.type_id = pt.id;
                                   QUERY PLAN                                    
---------------------------------------------------------------------------------
 Hash Join  (cost=38.58..63.74 rows=1200 width=64)
   Hash Cond: (p.type_id = pt.id)
   ->  Seq Scan on products p  (cost=0.00..22.00 rows=1200 width=36)
   ->  Hash  (cost=22.70..22.70 rows=1270 width=36)
         ->  Seq Scan on product_types pt  (cost=0.00..22.70 rows=1270 width=36)

Исходная версия AlexKiriukha, :

explain SELECT
product_name, type_name FROM products p, product_types pt WHERE p.type_id = pt.id; QUERY PLAN

Hash Join (cost=38.58..63.74 rows=1200 width=64) Hash Cond: (p.type_id = pt.id) -> Seq Scan on products p (cost=0.00..22.00 rows=1200 width=36) -> Hash (cost=22.70..22.70 rows=1270 width=36) -> Seq Scan on product_types pt (cost=0.00..22.70 rows=1270 width=36) (5 rows)

=# explain SELECT product_name, type_name FROM products p JOIN product_types pt ON p.type_id = pt.id; QUERY PLAN

Hash Join (cost=38.58..63.74 rows=1200 width=64) Hash Cond: (p.type_id = pt.id) -> Seq Scan on products p (cost=0.00..22.00 rows=1200 width=36) -> Hash (cost=22.70..22.70 rows=1270 width=36) -> Seq Scan on product_types pt (cost=0.00..22.70 rows=1270 width=36)