Modify data

QuestDB is a time-series database optimized to append data.

For best performance, design your application to avoid having to frequently edit existing records.

If you need to, the UPDATE statement is intended for correcting data that was inserted incorrectly.

These are three alternatives to UPDATE that you may consider:

• Append newest state: Insert a newer state to replace an older one: This has the added advantage that you can query back in time to a previous state. It is also the basis of organizing data for bi-temporality.

• Replace a table: Create a new table with the new data you need, drop the old one and rename.

• Delete by dropping partitions: Create your time-series tables with partitions, then delete the ones you no longer need.

note

Any time you are performing database modification, please remember to backup your database!

Append newest state

Using the timestamp field

Here's a worked example using the timestamp column:

CREATE TABLE takeaway_order (

ts TIMESTAMP,

id SYMBOL,

status SYMBOL)

timestamp(ts);

INSERT INTO takeaway_order VALUES (now(), 'order1', 'placed');

INSERT INTO takeaway_order VALUES (now(), 'order2', 'placed');

INSERT INTO takeaway_order VALUES (now(), 'order1', 'cooking');

INSERT INTO takeaway_order VALUES (now(), 'order1', 'in-transit');

INSERT INTO takeaway_order VALUES (now(), 'order1', 'arrived');

INSERT INTO takeaway_order VALUES (now(), 'order3', 'placed');

INSERT INTO takeaway_order VALUES (now(), 'order3', 'cooking');

INSERT INTO takeaway_order VALUES (now(), 'order3', 'in-transit');

We join the latest timestamp of an order id against the rest of the data to obtain full details.

WITH

ts_takeaway_order AS (

SELECT

max(ts) AS ts,

id

FROM

takeaway_order GROUP BY id)

SELECT

o.*

FROM

ts_takeaway_order ts_o

INNER JOIN 'takeaway_order' o

ON ts_o.ts = o.ts

This results in the latest state for each order:

timestamp ts	id symbol	status symbol
2022-04-07T15:33:43.944922Z	order1	arrived
2022-04-07T15:33:37.370694Z	order2	placed
2022-04-07T15:33:50.829323Z	order3	in-transit

Using dedicated fields

If timestamps don't work for you here, you can also use an extra integer column called version, an extra boolean deleted column or similar.

Replace Table

Another alternative is to:

• Backup your database.
• Select only the data you want from an existing table into a new temporary one.
• Drop the original table.
• Rename the temporary table to the original table's name.

CREATE TABLE mytable_copy AS (

SELECT * FROM mytable WHERE column_value != 42

) TIMESTAMP(ts) PARTITION BY DAY;

DROP TABLE mytable;

RENAME table mytable_copy TO mytable;

Delete by Dropping Partitions

When you create tables with a timestamp, you may organise them into partitions using the CREATE TABLE .. PARTITION BY SQL statement. But first, backup your database.

You may then use the ALTER TABLE DROP PARTITION SQL statement to drop partitions you no longer need.