Run Analytical Queries on Sample Data by Using ScalarDB Analytics with PostgreSQL
This tutorial describes how to run analytical queries on sample data by using ScalarDB Analytics with PostgreSQL.
Overview​
This sample tutorial shows how you can run two types of queries: a single-table query and a multi-table query.
What you can do in this sample tutorial​
This sample tutorial shows how you can run the following types of queries:
- Read data and calculate summaries.
- Join tables that span multiple storages.
You can run any arbitrary query that PostgreSQL supports on the imported tables in this sample tutorial. Since ScalarDB Analytics with PostgreSQL supports all queries that PostgreSQL supports, you can use not only join, aggregation, filtering, and ordering as shown in the example, but also the window function, lateral join, or various analytical operations.
To see which types of queries PostgreSQL supports, see the PostgreSQL documentation.
Prerequisites​
- Docker 20.10 or later with Docker Compose V2 or later
- psql
Set up ScalarDB Analytics with PostgreSQL​
First, you must set up the database to run analytical queries with ScalarDB Analytics with PostgreSQL. If you haven't set up the database yet, please follow the instructions in Getting Started.
Schema details in ScalarDB​
In this sample tutorial, you have tables with the following schema in the ScalarDB database:
For reference, this diagram shows the following:
dynamons,postgresns, andcassandrans. Namespaces that are mapped to the back-end storages of DynamoDB, PostgreSQL, and Cassandra, respectively.dynamons.customer. A table that represents information about customers. This table includes attributes like customer key, name, address, phone number, and account balance.postgresns.orders. A table that contains information about orders that customers have placed. This table includes attributes like order key, customer key, order status, order date, and order priority.cassandrans.lineitem. A table that represents line items associated with orders. This table includes attributes such as order key, part key, supplier key, quantity, price, and shipping date.
Schema details in PostgreSQL​
By running the Schema Importer when setting up ScalarDB, you can import the table schema in the ScalarDB database into the PostgreSQL database. More precisely, for each namespace_name.table_name table in the ScalarDB database, you will have a foreign table for namespace_name._table_name and a view for namespace_name.table_name in the PostgreSQL database.
The created foreign table contains columns that are identical to the ScalarDB table and the transaction metadata columns that ScalarDB manages internally. Since the created view is defined to exclude the transaction metadata columns from the foreign table, the created view contains only the same columns as the ScalarDB table.
You can find the schema of the ScalarDB tables in schema.json. For example, the dynamons.customer table is defined as follows:
"dynamons.customer": {
"transaction": true,
"partition-key": [
"c_custkey"
],
"columns": {
"c_custkey": "INT",
"c_name": "TEXT",
"c_address": "TEXT",
"c_nationkey": "INT",
"c_phone": "TEXT",
"c_acctbal": "DOUBLE",
"c_mktsegment": "TEXT",
"c_comment": "TEXT"
}
},
To see the foreign table for dynamons._customer in the PostgreSQL database, run the following command and enter your PostgreSQL user password when prompted:
psql -U postgres -h localhost test -c '\d dynamons._customer';
After entering your password, you should see the following output, which shows the same c_ columns as in the dynamons.customer table:
Foreign table "dynamons._customer"
Column | Type | Collation | Nullable | Default | FDW options
------------------------+------------------+-----------+----------+---------+-------------
c_custkey | integer | | | |
c_name | text | | | |
c_address | text | | | |
c_nationkey | integer | | | |
c_phone | text | | | |
c_acctbal | double precision | | | |
c_mktsegment | text | | | |
c_comment | text | | | |
tx_id | text | | | |
tx_version | integer | | | |
tx_state | integer | | | |
tx_prepared_at | bigint | | | |
tx_committed_at | bigint | | | |
before_tx_id | text | | | |
before_tx_version | integer | | | |
before_tx_state | integer | | | |
before_tx_prepared_at | bigint | | | |
before_tx_committed_at | bigint | | | |
before_c_name | text | | | |
before_c_address | text | | | |
before_c_nationkey | integer | | | |
before_c_phone | text | | | |
before_c_acctbal | double precision | | | |
before_c_mktsegment | text | | | |
before_c_comment | text | | | |
Server: multi_storage_dynamodb
FDW options: (namespace 'dynamons', table_name 'customer')
As you can see in the foreign table, the table also contains the transaction metadata columns. These columns are required to ensure the Read Committed isolation level.
To see the view for dynamons.customer, run the following command and enter your PostgreSQL user password when prompted:
psql -U postgres -h localhost test -c '\d dynamons.customer';
After entering your password, you should see the following output:
View "dynamons.customer"
Column | Type | Collation | Nullable | Default
--------------+------------------+-----------+----------+---------
c_custkey | integer | | |
c_name | text | | |
c_address | text | | |
c_nationkey | integer | | |
c_phone | text | | |
c_acctbal | double precision | | |
c_mktsegment | text | | |
c_comment | text | | |
The column definitions in this view are the same as the original table in the ScalarDB database. This view is created based on the foreign table explained above to expose only the valid data with the Read Committed isolation level by interpreting the transaction metadata columns.
Normally, you don't need to access the foreign tables directly. Instead, you can equate the views with the tables in the ScalarDB database.
For details about type mapping between ScalarDB and PostgreSQL, see Data-type mapping between ScalarDB and other databases.
Run analytical queries​
The following sections describe how to read data, calculate summaries, and join tables that span multiple storages.
Read data and calculate summaries​
You can run a query that reads data from cassandrans.lineitem, with the actual data stored in the Cassandra back-end, and calculates several summaries of the ordered line items by aggregating the data.
To run the query, log in to the psql terminal by running the following command:
psql -U postgres -h localhost test
After entering your password, enter the following query into the psql terminal:
SELECT
l_returnflag,
l_linestatus,
sum(l_quantity) AS sum_qty,
sum(l_extendedprice) AS sum_base_price,
sum(l_extendedprice * (1 - l_discount)) AS sum_disc_price,
sum(l_extendedprice * (1 - l_discount) * (1 + l_tax)) AS sum_charge,
avg(l_quantity) AS avg_qty,
avg(l_extendedprice) AS avg_price,
avg(l_discount) AS avg_disc,
count(*) AS count_order
FROM
cassandrans.lineitem
WHERE
to_date(l_shipdate, 'YYYY-MM-DD') <= date '1998-12-01' - 3
GROUP BY
l_returnflag,
l_linestatus
ORDER BY
l_returnflag,
l_linestatus;
You should see the following output:
l_returnflag | l_linestatus | sum_qty | sum_base_price | sum_disc_price | sum_charge | avg_qty | avg_price | avg_disc | count_order
--------------+--------------+---------+--------------------+--------------------+--------------------+---------------------+--------------------+---------------------+-------------
A | F | 1519 | 2374824.6560430005 | 1387363.5818635763 | 1962762.9341866106 | 26.6491228070175439 | 41663.590456894744 | 0.4150182982456142 | 57
N | F | 98 | 146371.22954200002 | 85593.92837883368 | 121041.52567369482 | 32.6666666666666667 | 48790.409847333336 | 0.4098473333333333 | 3
N | O | 5374 | 8007373.247144971 | 4685645.630765834 | 6624209.157932242 | 24.4272727272727273 | 36397.15112338623 | 0.414759749999999 | 220
R | F | 1461 | 2190869.967642001 | 1284177.8484816086 | 1814150.7929095028 | 25.1896551724137931 | 37773.62013175864 | 0.41323520689655185 | 58
(4 rows)
Join tables that span multiple storages​
You can also run a query to join tables that are connected to the three back-end storages and calculate the unshipped orders with the highest revenue on a particular date.
To run the query, log in to the psql terminal by running the following command:
psql -U postgres -h localhost test
After entering your password, enter the following query into the psql terminal:
SELECT
l_orderkey,
sum(l_extendedprice * (1 - l_discount)) AS revenue,
o_orderdate,
o_shippriority
FROM
dynamons.customer,
postgresns.orders,
cassandrans.lineitem
WHERE
c_mktsegment = 'AUTOMOBILE'
AND c_custkey = o_custkey
AND l_orderkey = o_orderkey
AND o_orderdate < '1995-03-15'
AND l_shipdate > '1995-03-15'
GROUP BY
l_orderkey,
o_orderdate,
o_shippriority
ORDER BY
revenue DESC,
o_orderdate,
l_orderkey
LIMIT 10;
You should see the following output:
l_orderkey | revenue | o_orderdate | o_shippriority
------------+--------------------+-------------+----------------
1071617 | 128186.94002748765 | 1995-03-10 | 0
1959075 | 33104.49713665398 | 1994-12-23 | 0
430243 | 19476.107574179696 | 1994-12-24 | 0
(3 rows)
Stop ScalarDB Analytics with PostgreSQL and the database​
To stop ScalarDB Analytics with PostgreSQL and the database, stop the Docker container by running the following command:
docker-compose down