Timestamp function

timestamp(columnName) elects a designated timestamp:

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

:::note

• 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.

• There are two timestamp resolutions available in QuestDB: microseconds and nanoseconds. See Timestamp resolution for more details. :::

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.

Optimization with WHERE clauses

When filtering on a designated timestamp column in WHERE clauses, QuestDB automatically optimizes the query by applying time-based partition filtering. This optimization also works with subqueries that return timestamp values.

For example:

SELECT *
FROM trades
WHERE timestamp > (SELECT min(timestamp) FROM trades)
  AND timestamp < (SELECT max(timestamp) FROM trades);

In this case, if ts is the designated timestamp column, QuestDB will optimize the query by:

1. Evaluating the subqueries to determine the time range
2. Using this range to filter partitions before scanning the data
3. Applying the final timestamp comparison on the remaining records

This optimization applies to timestamp comparisons using:

• Greater than (>)
• Less than (<)
• Equals (=)
• Greater than or equal to (>=)
• Less than or equal to (<=)

Examples

During a CREATE operation

The following creates a table with designated timestamp.

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 trades table.

(SELECT cast(dateTime AS TIMESTAMP) ts, symbol, price FROM trades) timestamp(ts);

Although the trades 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.

SELECT ts, avg(price) FROM
(SELECT cast(dateTime AS TIMESTAMP) ts, price FROM trades) timestamp(ts)
SAMPLE BY 1d;

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

SELECT ts, avg(price) FROM
(SELECT ts, price FROM unordered_trades ORDER BY ts) timestamp(ts)
SAMPLE BY 1d;