在创建 View 的时候,PostgreSQL是否也为对应的查询创建了prepared statement?还是每次访问 View 时都重新生成查询执行计划?
最佳答案
不是,每次使用 View 都会构造一个查询计划。即使 View 与其他表或 View 连接(您可以将 View 视为一种宏)。只需查看生成的查询计划:
CREATE table one
( one_id INTEGER NOT NULL PRIMARY KEY
, one_text text
);
INSERT INTO one (one_id,one_text)
SELECT gs, 'one_' || gs::integer
FROM generate_series (0,10,2) gs;
CREATE table two
( two_id INTEGER NOT NULL PRIMARY KEY
, two_text text
);
INSERT INTO two (two_id,two_text)
SELECT gs, 'two_' || gs::integer
FROM generate_series (0,10,3) gs;
VACUUM ANALYZE one;
VACUUM ANALYZE two;
CREATE VIEW silly_carth AS
SELECT o.one_id, o.one_text
, t.two_id, t.two_text
FROM one o
CROSS JOIN two t
;
EXPLAIN
SELECT * FROM silly_carth;
EXPLAIN
SELECT * FROM silly_carth WHERE one_id = two_id;
结果计划:
QUERY PLAN
------------------------------------------------------------------
Nested Loop (cost=0.00..2.41 rows=24 width=20)
-> Seq Scan on one o (cost=0.00..1.06 rows=6 width=10)
-> Materialize (cost=0.00..1.06 rows=4 width=10)
-> Seq Scan on two t (cost=0.00..1.04 rows=4 width=10)
(4 rows)
QUERY PLAN
------------------------------------------------------------------
Hash Join (cost=1.09..2.21 rows=4 width=20)
Hash Cond: (o.one_id = t.two_id)
-> Seq Scan on one o (cost=0.00..1.06 rows=6 width=10)
-> Hash (cost=1.04..1.04 rows=4 width=10)
-> Seq Scan on two t (cost=0.00..1.04 rows=4 width=10)
(5 rows)
关于sql - Postgres - 观点是否得到准备好的陈述的支持?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/34807950/