Timestamp function

timestamp(columnName) elects a designated timestamp:

• during a CREATE TABLE operation
• during a SELECT operation (dynamic timestamp)
• when ingesting data via ILP, for tables that do not already exist in QuestDB, partitions are applied automatically by day by default with a timestamp column

info

Checking if tables contain a designated timestamp column can be done via the tables() and table_columns() functions which are described in the meta functions documentation page.

Syntax

During a CREATE operation

Create a designated timestamp column during table creation. For more information, refer to the CREATE TABLE section.

During a SELECT operation

Creates a designated timestamp column in the result of a query. Assigning a timestamp in a SELECT statement (dynamic timestamp) allows for time series operations such as LATEST BY, SAMPLE BY or LATEST BY on tables which do not have a designated timestamp assigned.

Examples

During a CREATE operation

The following creates a table with designated timestamp.

Create table

CREATE TABLE

temperatures(ts timestamp, sensorID symbol, sensorLocation symbol, reading double)

timestamp(ts);

During a SELECT operation

The following will query a table and assign a designated timestamp to the output. Note the use of brackets to ensure the timestamp clause is applied to the result of the query instead of the whole readings table.

Dynamic timestamp

(SELECT cast(dateTime AS TIMESTAMP) ts, device, value FROM readings) timestamp(ts);

Although the readings table does not have a designated timestamp, we are able to create one on the fly. Now, we can use this into a subquery to perform timestamp operations.

Dynamic timestamp subquery

SELECT ts, avg(value) FROM

(SELECT cast(dateTime AS TIMESTAMP) ts, value FROM readings) timestamp(ts)

SAMPLE BY 1d;

If the data is unordered, it is important to order it first.

Dynamic timestamp - unordered data

SELECT ts, avg(value) FROM

(SELECT ts, value FROM unordered_readings ORDER BY ts) timestamp(ts)

SAMPLE BY 1d;