The Distributed SQL Blog

Thoughts on distributed databases, open source and cloud native

Distributed SQL Tips and Tricks – Feb 14, 2020

VP Developer Relations

Welcome to this week’s tips and tricks blog where we recap some distributed SQL questions from around the Internet. We’ll also review upcoming events, new documentation and blogs that have been published since the last post. Got questions? Make sure to ask them on our YugabyteDB Slack channel, Forum, GitHub or Stackoverflow. Ok, let’s dive right in:

How can I get the JSON output of distinct columns?

This can be done in YugabyteDB with a combination of aggregation and PostgreSQL’s JSON functions. For example, let’s say we have the following table called students with the data below:

Example table PostgreSQL compatible YugabyteDB

To output to JSON by distinct columns, execute the following:

select 
    person_key,
    json_build_object(
        'age', age,
        'gender', gender,
        'email', json_agg(email order by id)
    ) js
from students
group by person_key, age, gender
order by person_key;

Which should output:

JSON output in YugabyteDB distributed SQL database

How do I issue a query that ranks items based on total sales?

Because YugabyteDB is PostgreSQL-compatible, just like in PostgreSQL, in YugabyteDB you can rank items based on total sales by using the RANK function. For example, let’s say we have the following table called product_sales with the data below:

table example product_sales to be used in distributed SQL rank function

We can use the following query which makes use of the RANK window function.

SELECT 
    business_unit, 
    product_name,
    SUM(sales) AS sales,
    RANK() OVER(ORDER BY SUM(sales) DESC) ranking
FROM product_sales
GROUP BY business_unit, product_name
ORDER BY ranking, business_unit

This results in the following ranking based on total sales:

output of ranking function in distributed sql example

In YugabyteDB, do TRUNCATE and DELETE work like they do in PostgreSQL?

Yes. In general, to remove data from a table, you’ll want to use the DELETE statement with a WHERE clause. However, for a large table, it is often more efficient to use the TRUNCATE TABLE statement. Why? Because the TRUNCATE TABLE statement removes all rows from a table without scanning it. This is the reason why it is faster than the DELETE statement. TRUNCATE is also able to operate on more than one table with a single command.

How do I issue an UPDATE statement and selectively replace specific characters in records that match given criteria?

Just like in PostgreSQL, in YugabyteDB one way you can do this is by using the REGEX_REPLACE function. For example, let’s say we have a table called product_registrations and unfortunately the zeros in the serial numbers were accidentally inputted as “o”.

example of when to use REGEX_REPLACE in distributed sql database

By using the REGEX_REPLACE function we can surgically make the correct substitution.

UPDATE product_registrations
SET serial_number = REGEXP_REPLACE(serial_number, '^snoo', 'sn00');

The new output should look like this:

example after using REGEX_REPLACE function in distributed sql db

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VP Developer Relations