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.
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.
However, enumerating subset of SELECT columns in the GROUP BY clause is
redundant and therefore unnecessary. The same SQL in QuestDB SQL-dialect can be
written as:
Implicit HAVING#
Let's look at another more complex example using HAVING in standard SQL.
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: