CREATE INDEX command to construct an index on a table or a materialized view.
What are indexes?
Indexes in a database are designed to increase the speed at which the database management system (DBMS) can locate and retrieve the desired data from a table or a materialized view. Indexes are usually created on one or more columns in a table and can greatly improve the performance of queries, particularly for tables that are large in size or accessed frequently. Indexes are usually created on non-primary columns to speed up point-select queries on those columns.
Benefits of using indexes
In general, using indexes can significantly enhance the performance and efficiency of the system.
When to use indexes
Indexes can be particularly useful for optimizing the performance of queries that retrieve a small number of records from a large dataset. In RisingWave, indexes can speed up batch queries.
CREATE INDEX index_name ON object_name ( index_column [ ASC | DESC ], [, ...] )
[ INCLUDE ( include_column [, ...] ) ]
[ DISTRIBUTED BY ( distributed_column [, ...] ) ];
|Parameter or clause
|The name of the index to be created.
|The name of the table or materialized view where the index is created.
|The name of the column on which the index is created.
|Sort the data returned in descending order.
|Specify the columns to include in the index as non-key columns.
|DISTRIBUTED BY clause
|Specify the index distribution key.
Let's create two tables,
CREATE TABLE customers (
PRIMARY KEY (c_custkey)
CREATE TABLE orders (
PRIMARY KEY (o_orderkey)
If you want to speed up the query of fetching a customer record by the phone number, you can build an index on the
c_phone column in the
CREATE INDEX idx_c_phone on customers(c_phone);
SELECT * FROM customers where c_phone = '123456789';
SELECT * FROM customers where c_phone in ('123456789', '987654321');
If you want to speed up the query of fetching all the orders of a customer by the customer key, you can build an index on the
o_custkey column in the
CREATE INDEX idx_o_custkey ON orders(o_custkey);
SELECT * FROM customers JOIN orders ON c_custkey = o_custkey
WHERE c_phone = '123456789';
How to decide which columns to include?
By default, RisingWave creates an index that includes all columns of a table or a materialized view if you omit the
INCLUDE clause. This differs from the standard PostgreSQL. Why? RisingWave's design as a cloud-native streaming database includes several key differences from PostgreSQL, including the use of an object store for more cost-effective storage and the desire to make index creation as simple as possible for users who are not experienced with database systems. By including all columns, RisingWave ensures that an index will cover all of the columns touched by a query and eliminates the need for a primary table lookup, which can be slower in a cloud environment due to network communication. However, RisingWave still provides the option to include only specific columns using the
INCLUDE clause for users who wish to do so.
If your queries only access certain columns, you can create an index that includes only those columns. The RisingWave optimizer will automatically select the appropriate index for your query.
-- Create an index that only includes necessary columns
CREATE INDEX idx_c_phone1 ON customers(c_phone) INCLUDE (c_name, c_address);
-- RisingWave will automatically use index idx_c_phone1 for the following query since it only access the indexed columns.
SELECT c_name, c_address FROM customers WHERE c_phone = '123456789';
You can use the
EXPLAIN command to view the execution plan.
How to decide the index distribution key?
RisingWave will use the first index column as the
distributed_column by default if you omit the
DISTRIBUTED BY clause. RisingWave distributes the data across multiple nodes and uses the
distributed_column to determine how to distribute the data based on the index. If your queries intend to use indexes but only provide the prefix of the
index_column, it could be a problem for RisingWave to determine which node to access the index data from. To address this issue, you can specify the
distributed_column yourself, ensuring that these columns are the prefixes of the
-- Create an index with specified distributed columns
CREATE INDEX idx_c_phone2 ON customers(c_name, c_nationkey) DISTRIBUTED BY (c_name);
SELECT * FROM customers WHERE c_name = 'Alice';
Indexes on expressions
RisingWave supports creating indexes on expressions. Indexes on expressions are normally used to improve the performance of queries for frequently used expressions. To create an index on an expression, use the syntax:
CREATE INDEX index_name ON object_name (expression(column_name));
For example, if you often perform queries like this:
SELECT * FROM people WHERE (first_name || ' ' || last_name) = 'John Smith';
then you might want to create an index like the following to improve the performance of such queries:
CREATE INDEX people_names ON people ((first_name || ' ' || last_name));
DROP INDEX — Remove an index constructed on a table or a materialized view.