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Creating materialised view using table definition in cassandra
A materialised is defined as a database object that contains the results of a particular query. It could be called as a subset of a table. Any changes in the base table would be reflected in the materialised view.
Syntax
CREATE MATERIALISED VIEW view_name AS SELECT * FROM table_name WHERE column_name IS NOT NULL PRIMARY KEY (provide_primary_key)
Here,
view_name is the name of the materialised view,
table_name is the base table,
column_name are the columns
provide_primary_key are the primary keys for the base table.
Example 1
In this example, we are gonna have a look on how to create a materialised view for a table.
Algorithm
Step 1 − Create a keyspace
Step 2 − Create table within the keyspace
Step 3 − Create materialised view within the keyspace
Step 4 − Select data from table the table
Step 5 − Verify the values to be not null
Step 6 − Provide primary key.
Step 7 − Values inserted into the table
Step 8 − Select values from table to get the desired output.
Code
CREATE KEYSPACE position WITH REPLICATION= {'class': 'simplestrategy','replication_factor':1}; #keyspace is created CREATE TABLE position.employee (e_id int,e_name char(50),dept char(50),salary int) #table created inside keyspace CREATE MATERIALISED VIEW position.cell #materialised view named cell is created AS SELECT e_id,e_name,dept,salary FROM employee #data is selected WHERE e_id IS NOT NULL AND e_name IS NOT NULL #verifying that primary key values must not be null PRIMARY KEY (e_id);#primary key provided INSERT INTO employee values(1,'rahul','developer',40000), (2,'monu','hr',50000), (3,'aman','consulting',60000);#data is inserted SELECT * FROM cell;
Output
e_id |
e_name |
dept |
salary |
---|---|---|---|
1 |
rahul |
developer |
40000 |
2 |
monu |
hr |
50000 |
3 |
aman |
consulting |
60000 |
Example 2
In this example, we are going to see the effect of the primary key as to create a valid materialised view.
Here, we are going to create a table first with the primary key known.
Input TABLE
PLANT
P_name |
fruit |
taste |
---|---|---|
mango_tree |
mango |
sweet |
lemon_tree |
lemon |
sour |
apple_tree |
apple |
sweet |
P_name = primary key
Case 1 − Materialised view allowed
Algorithm
Step 1 − Create materialised view
Step 2 − Select value from base table
Step 3 − Verify the values to be not null
Step 4 − Provide primary key
Step 5 − Select values for materialised view
Code
CREATE MATERIALISED VIEW nature AS #materialised view created SELECT * FROM plant #value selected WHERE p_name IS NOT NULL #condition check for not null PRIMARY KEY (p_name);# primary key provided SELECT * FROM nature;
Output
Nature
P_name |
fruit |
taste |
---|---|---|
mango_tree |
mango |
sweet |
lemon_tree |
lemon |
sour |
apple_tree |
apple |
sweet |
Case 2 − Materialised view not allowed −
Algorithm
Step 1 − Create materialised view
Step 2 − Select value from base table
Step 3 − Verify the values to be not null
Step 4 − Provide primary key
Code
CREATE MATERIALISED VIEW nature AS#materialised view created SELECT * FROM plant#value selected WHERE p_name IS NOT NULL AND fruit IS NOT NULL #condition check for not null PRIMARY KEY (fruit);# primary key provided
Output
Invalid Primary key
Conclusion
Creating materialised view is as making a subset of a table so as to contain the result of a particular query. In first example, we have created materialised view by creating keyspace whereas in second example, we have focused on creating a valid materialised view by having two cases in which case 1 having the materialised view allowed and case 2 having it not allowed and as a result also found the importance of primary key