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Announcing ksqlDB 0.9.0

We’re pleased to announce the release of ksqlDB 0.9.0! This version includes support for multi-join statements, enhanced LIKE expressions, and a host of usability improvements. We’ll go through a few of the key changes, but you can see the changelog for a detailed list of all fixes and improvements.

Multi-join expression support

ksqlDB has allowed you to use queries with joins since its inception, but multiple joins in a single statement were not possible.

Starting today, you can collapse multiple joins into a single statement. This is crucial not only because it makes ksqlDB programs more concise, but also because it reduces the number of intermediate streams and topics for temporary joined data and is a much more efficient way to execute multiple joins.

table customers | stream orders | table items ➝ customer_orders_report

For example, let’s say we have two tables (customers and items) and one stream (orders) that have purchasing orders from an online store.

ksql> CREATE TABLE customers (customerid STRING, customername STRING) WITH (KAFKA_TOPIC='customers', VALUE_FORMAT='json', KEY='customerid'); 

ksql> CREATE TABLE items (itemid STRING, itemname STRING) WITH (KAFKA_TOPIC='items', VALUE_FORMAT='json', KEY='itemid');

ksql> CREATE STREAM orders (orderid STRING, customerid STRING, itemid STRING, purchasedate STRING) WITH (KAFKA_TOPIC='orders', VALUE_FORMAT='json', KEY='orderid');
ℹ️ Note: As of 0.10, the KEY property in the WITH clause is not supported. To specify a key, use the PRIMARY KEY keyword for tables, and the KEY keyword for streams in the schema column definition. For example:
CREATE TABLE customers (customerid STRING PRIMARY KEY, ...)
CREATE STREAM orders (orderid STRING KEY, …)

With these example records:

# customers
{"customerid": "1", "customername": "Adrian Garcia"}
{"customerid": "2", "customername": "Robert Miller"}
{"customerid": "3", "customername": "Brian Smith"}

# items
{"itemid": "1", "itemname": "Television 60-in"}
{"itemid": "2", "itemname": "Laptop 15-in"}
{"itemid": "3", "itemname": "Speakers"} 

# orders
{"orderid": "1", "customerid": "1", "itemid": "1", "purchasedate": "2020-05-01"}
{"orderid": "2", "customerid": "1", "itemid": "2", "purchasedate": "2020-05-01"}
{"orderid": "3", "customerid": "2", "itemid": "1", "purchasedate": "2020-05-01"}
{"orderid": "4", "customerid": "3", "itemid": "1", "purchasedate": "2020-05-03"}
{"orderid": "5", "customerid": "2", "itemid": "3", "purchasedate": "2020-05-03"}
{"orderid": "6", "customerid": "2", "itemid": "2", "purchasedate": "2020-05-05"}

…let’s generate a report of all orders and customers who made purchases, and write that report in the topic customer_orders_report. This should include customer and item names.

Using the old way (ksqlDB 0.8.x and lower), you would need to create a temporary stream to join customers - orders records, then create your final stream to join the temporary_stream - items to generate the report:

ksql> CREATE STREAM tmp_join AS
SELECT customers.customerid AS customerid, customers.customername, orders.orderid, orders.itemid, orders.purchasedate
FROM orders 
INNER JOIN customers ON orders.customerid = customers.customerid

ksql> CREATE STREAM customers_orders_report AS
SELECT customerid, customername, orderid, items.itemname, purchasedate
FROM tmp_join
LEFT JOIN items ON tmp_join.itemid = items.itemid

With ksqlDB 0.9.0, just create the final stream with the joins you need to create the report:

ksql> CREATE STREAM customers_orders_report AS
SELECT customers.customerid AS customerid, customers.customername, orders.orderid, tems.itemid, items.itemname, orders.purchasedate
FROM orders 
LEFT JOIN customers ON orders.customerid = customers.customerid
LEFT JOIN items ON orders.itemid = items.itemid

Take a look at this query, which reads data from your previous report. It shows columns from customers, items, and orders.

ksql> SELECT customername, itemname, purchasedate FROM customers_orders_report EMIT CHANGES;
| Adrian Garcia    | Television 60"   | 2020-05-01   |
| Adrian Garcia    | Laptop 15"       | 2020-05-01   |
| Robert Miller    | Television 60"   | 2020-05-01   |
| Brian Smith      | Television 60"   | 2020-05-03   |
| Robert Miller    | Speakers         | 2020-05-03   |
| Robert Miller    | Laptop 15"       | 2020-05-05   |

This also works with any previously supported joins, such as inner, left, and outer joins. There is no limit to the number of joins in a single statement. Normal restrictions apply (e.g., you can’t repartition tables).

More powerful LIKE expressions

ksqlDB supports pattern matching using LIKE expressions. Until now, the wildcard character, %, was supported only at the start and end of the pattern expression.

With ksqlDB 0.9.0, LIKE expressions support the % character at any position. You can also use the underscore (_) character to match exactly one character in the value.

Furthermore, the new ESCAPE clause has been added to complement LIKE expressions. ESCAPE allows you to specify an escape character in the pattern, so that special characters in the condition are interpreted literally.

This is what a LIKE clause looks like:

FROM ...
WHERE field [NOT] LIKE condition [ESCAPE escape_string]

The following statement queries all records that contain a message with 90—99% of CPU usage (assuming there are no letters next to the “9” number):

WHERE message LIKE “%cpu = 9_/%%” ESCAPE ‘/’;

And there’s more!

A new built-in function, COALESCE, as well as various bug fixes and other improvements are included in this release. See the full list of fixes and improvements in the changelog.

If you haven’t already, join our #ksqldb Confluent Community Slack channel and get started with ksqlDB today!

Sergio Peña is a software engineer on the ksqlDB Engineering Team at Confluent. Prior to joining Confluent, Sergio was part of the Apache Hive™, Sentry™, and Parquet™ engineering teams at Cloudera, working on security, SQL performance, and file format improvements for Cloudera platforms. He was also an engineer at Gazzang (acquired by Cloudera), where he led the development and design of Gazzang zNcrypt, a big data and cloud encryption tool for Apache™ Hadoop® and other big data services.

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