I'm wondering if it's generally more efficient to use a materialized view for joining tables rather than a Common Table Expression (CTE). For example, if I have tables foo
and bar
that are joined and then later joined with baz
, would a materialized view of foo
and bar
be faster because it can track changes, as opposed to a CTE which doesn't maintain state? Here's a simplified example with task
and task_priority
tables:
dev=> create table task (id int, detail text);
dev=> create table task_priority (task_id int, priority int);
dev=> create table baz (id int, info text);
-- Materialized view approach
dev=> create materialized view task_with_prioritizations as
select task.id, task.detail, task_priority.priority
from task
left join task_priority on task.id = task_priority.task_id;
-- CTE approach
dev=> with task_cte as (
select task.id, task.detail, task_priority.priority
from task
left join task_priority on task.id = task_priority.task_id
)
select task_cte.*, baz.info
from task_cte
join baz on task_cte.id = baz.id;
Does the materialized view have an advantage because it 'knows' the state of the join, or would recalculating everything with a CTE be just as efficient?
André Falk
Asked on Dec 20, 2023
The performance of using a materialized view versus a CTE can depend on various factors such as the filters applied, the presence of indexes, the size of the data, and whether the data is in cache or on disk. Materialized views have the advantage of pre-computing joins and maintaining state, which can be faster for subsequent queries. However, this is not always the case, and sometimes querying underlying tables with filters and then performing joins in real-time can be more efficient, especially if the materialized view would result in a very large dataset.
It's important to compare the query plans using tools like EXPLAIN
to understand the execution plans and make an informed decision. Additionally, the specific requirements of the use case, such as the need for real-time data or the frequency of data changes, should also be considered when choosing between a materialized view and a CTE.