CHANGES

The CHANGES clause allows querying the change tracking metadata for a table within a defined time interval. Please note that the time interval must fall within the data retention period (defaulted to 24 hours). To define a time interval, use the AT keyword to specify a time point as the start of the interval, with the current time being applied as the default end of the interval. If you wish to specify a past time as the end of the interval, use the END keyword in conjunction with the AT keyword to set the interval.

Syntax

SELECT ...
FROM ...
   CHANGES ( INFORMATION => { DEFAULT | APPEND_ONLY } )
   AT ( { TIMESTAMP => <timestamp> |
          OFFSET => <time_interval> |
          SNAPSHOT => '<snapshot_id>' |
          STREAM => <stream_name> } )

    [ END ( { TIMESTAMP => <timestamp> |
             OFFSET => <time_interval> |
             SNAPSHOT => '<snapshot_id>' } ) ]

Enabling Change Tracking

The CHANGES clause requires that the Fuse engine option change_tracking must be set to true on the table. For more information about the change_tracking option, see Fuse Engine Options.

-- Enable change tracking for table 't'
ALTER TABLE t SET OPTIONS(change_tracking = true);

Examples

This example demonstrates the use of the CHANGES clause, allowing for the tracking and querying of changes made to a table:

1. Create a table to store user profile information and enable change tracking.

   CREATE TABLE user_profiles (
       user_id INT,
       username VARCHAR(255),
       bio TEXT
   ) change_tracking = true;
   
   INSERT INTO user_profiles VALUES (1, 'john_doe', 'Software Engineer');
   INSERT INTO user_profiles VALUES (2, 'jane_smith', 'Marketing Specialist');
   

2. Create a stream to capture profile updates, then update an exiting profile and insert a new one.

   CREATE STREAM profile_updates ON TABLE user_profiles APPEND_ONLY = TRUE;
   
   UPDATE user_profiles SET bio = 'Data Scientist' WHERE user_id = 1;
   INSERT INTO user_profiles VALUES (3, 'alex_wong', 'Data Analyst');
   

3. Query changes in user profiles by the stream.

   -- Return all changes in user profiles captured in the stream
   SELECT *
   FROM user_profiles
   CHANGES (INFORMATION => DEFAULT)
   AT (STREAM => profile_updates);
   
   ┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
   │     user_id     │     username     │        bio        │   change$action  │              change$row_id             │ change$is_update │
   ├─────────────────┼──────────────────┼───────────────────┼──────────────────┼────────────────────────────────────────┼──────────────────┤
   │               1 │ john_doe         │ Data Scientist    │ INSERT           │ 69cffb02264144c384d56f7b6cedee41000000 │ true             │
   │               3 │ alex_wong        │ Data Analyst      │ INSERT           │ 59f315c8655c49eab35ba1959e269430000000 │ false            │
   │               1 │ john_doe         │ Software Engineer │ DELETE           │ 69cffb02264144c384d56f7b6cedee41000000 │ true             │
   └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
   
   -- Return appended rows in user profiles captured in the stream
   SELECT *
   FROM user_profiles
   CHANGES (INFORMATION => APPEND_ONLY)
   AT (STREAM => profile_updates);
   
   ┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
   │     user_id     │     username     │        bio       │ change$action │ change$is_update │              change$row_id             │
   ├─────────────────┼──────────────────┼──────────────────┼───────────────┼──────────────────┼────────────────────────────────────────┤
   │               3 │ alex_wong        │ Data Analyst     │ INSERT        │ false            │ 59f315c8655c49eab35ba1959e269430000000 │
   └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
   

4. Query changes between a snapshot and a timestamp with both the AT and END keywords.

-- Step 6: Take a snapshot of the user profile data.
SELECT snapshot_id, timestamp
FROM FUSE_SNAPSHOT('default', 'user_profiles');

┌───────────────────────────────────────────────────────────────┐
│            snapshot_id           │          timestamp         │
├──────────────────────────────────┼────────────────────────────┤
│ 6a11c94433714970895edd38577ac8b0 │ 2024-04-10 02:51:39.422832 │
│ 53dc4750af92423da91c50dcee547cfb │ 2024-04-10 02:51:39.399568 │
│ 910af7424f764891b0c6fa60aa99fc3a │ 2024-04-10 02:50:14.522416 │
│ 1225000916f44819a0d23178b2d0d1af │ 2024-04-10 02:50:14.500417 │
└───────────────────────────────────────────────────────────────┘

SELECT *
FROM user_profiles
CHANGES (INFORMATION => DEFAULT)
AT (SNAPSHOT => '1225000916f44819a0d23178b2d0d1af')
END (TIMESTAMP => '2024-04-10 02:51:39.399568'::TIMESTAMP);

┌──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│     user_id     │     username     │          bio         │   change$action  │              change$row_id             │ change$is_update │
├─────────────────┼──────────────────┼──────────────────────┼──────────────────┼────────────────────────────────────────┼──────────────────┤
│               1 │ john_doe         │ Data Scientist       │ INSERT           │ 69cffb02264144c384d56f7b6cedee41000000 │ true             │
│               1 │ john_doe         │ Software Engineer    │ DELETE           │ 69cffb02264144c384d56f7b6cedee41000000 │ true             │
│               2 │ jane_smith       │ Marketing Specialist │ INSERT           │ 3db484ac18174223851dc9de22f6bfec000000 │ false            │
└──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘