SQL extensions

QuestDB attempts to implement standard ANSI SQL. We also attempt to be PostgreSQL compatible, although some of it is work in progress. This page presents the main extensions we bring to SQL and the main differences that one might find in SQL but not in QuestDB's dialect.

SQL extensions#

We have extended SQL language to support our data storage model and simplify semantics of time series queries.

LATEST BY#

LATEST BY is a clause introduced to help perform UPDATE and DELETE operations within an append-only framework.

SAMPLE BY#

SAMPLE BY for time based aggregations with an efficient syntax. The short query below will return the simple average balance from a list of accounts by one month buckets.

Using SAMPLE BY
select avg(balance) from accounts sample by 1M

Timestamp search#

Timestamp search can be performed with regular operators, e.g >, <= etc. However, QuestDB provides a native notation which is faster and less verbose.

Differences from standard SQL#

Optionality of SELECT * FROM#

In QuestDB select * from is optional. So SELECT * FROM tab; achieves the same effect as tab; While select * from makes SQL look more complete, there are examples where its optionality makes things a lot easier to read.

Optionality of GROUP BY#

The GROUP BY clause is optional and can be omitted as the QuestDB optimiser derives group-by implementation from SELECT clause.

In standard SQL, users might write a query like the below.

SELECT a, b, c, d, sum(e) FROM tab GROUP BY a, b, c, d;

However, enumerating subset of SELECT columns in the GROUP BY clause redundant and therefore unnecessary. The same SQL in QuestDB SQL-dialect can be written as:

SELECT a, b, c, d, sum(e) FROM tab;

Implicit HAVING#

Let's look at another more complex example using HAVING in standard SQL.

SELECT a, b, c, d, sum(e)
FROM tab
GROUP BY a, b, c, d
HAVING sum(e) > 100;

In QuestDB's dialect, select * from optionality and featherweight sub-queries come to the rescue to create a smaller, more readable query, without unnecessary repetitive aggregations. HAVING functionality can be obtained implicitly as follows:

(SELECT a, b, c, d, sum(e) s FROM tab) WHERE s > 100;