Create and use a materialized view
You can create a materialized view of a query to calculate and store results of an expensive operation, such as particular join, that you repeatedly run. When you issue queries specified by that materialized view, the optimizer rewrites the query based on it. This action saves reprocessing. Query performance improves.
In this task, you create and populate example tables. You create a materialized view of a join of the tables. Subsequently, when you run a query to join the tables, the query plan takes advantage of the precomputed join to accelerate processing. This task is over-simplified and is intended to show the syntax and output of a materialized view, not to demonstrate accelerated processing that results in a real-world task, which would process a large amount of data.
Create two tables:
CREATE TABLE emps ( empid INT, deptno INT, name VARCHAR(256), salary FLOAT, hire_date TIMESTAMP); CREATE TABLE depts ( deptno INT, deptname VARCHAR(256), locationid INT);
Insert some data into the tables for example purposes:
INSERT INTO TABLE emps VALUES (10001,101,'jane doe',250000,'2018-01-10'); INSERT INTO TABLE emps VALUES (10002,100,'somporn klailee',210000,'2017-12-25'); INSERT INTO TABLE emps VALUES (10003,200,'jeiranan thongnopneua',175000,'2018-05-05'); INSERT INTO TABLE depts VALUES (100,'HR',10); INSERT INTO TABLE depts VALUES (101,'Eng',11); INSERT INTO TABLE depts VALUES (200,'Sup',20);
Create a materialized view to join the tables:
CREATE MATERIALIZED VIEW mv1 AS SELECT empid, deptname, hire_date FROM emps JOIN depts ON (emps.deptno = depts.deptno) WHERE hire_date >= '2017-01-01';
Run a query that takes advantage of the precomputation performed by the
SELECT empid, deptname FROM emps JOIN depts ON (emps.deptno = depts.deptno) WHERE hire_date >= '2017-01-01' AND hire_date <= '2019-01-01';Output is:
+--------+-----------+ | empid | deptname | +--------+-----------+ | 10003 | Sup | | 10002 | HR | | 10001 | Eng | +--------+-----------+