Default Merge Engine (LastRow)

Overview

The Default Merge Engine behaves as a LastRow merge engine that retains the latest record for a given primary key. It supports all the operations: INSERT, UPDATE, DELETE. Additionally, the default merge engine supports Partial Update, which preserves the latest values for the specified update columns. If the 'table.merge-engine' property is not explicitly defined in the table properties when creating a Primary Key Table, the default merge engine will be applied automatically.

Example

Flink SQL

CREATE TABLE T (
    k  INT,
    v1 DOUBLE,
    v2 STRING,
    PRIMARY KEY (k) NOT ENFORCED
);

-- Insert
INSERT INTO T(k, v1, v2) VALUES (1, 1.0, 't1');
INSERT INTO T(k, v1, v2) VALUES (1, 1.0, 't2');
SELECT * FROM T WHERE k = 1;
-- Output:
+----+-----+----+
| k  | v1  | v2 |
+----+-----+----+
| 1  | 1.0 | t2 |
+----+-----+----+

-- Update
INSERT INTO T(k, v1, v2) VALUES (2, 2.0, 't2');
UPDATE T SET v1 = 4.0 WHERE k = 2;
SELECT * FROM T WHERE k = 2;
 -- Output:
+----+-----+----+
| k  | v1  | v2 |
+----+-----+----+
| 2  | 4.0 | t2 |
+----+-----+----+


-- Partial Update
INSERT INTO T(k, v1) VALUES (3, 3.0); -- set v1 to 3.0
SELECT * FROM T WHERE k = 3;
-- Output:
+----+-----+------+
| k  | v1  | v2   |
+----+-----+------+
| 3  | 3.0 | null |
+----+-----+------+
INSERT INTO T(k, v2) VALUES (3, 't3'); -- set v2 to 't3'
SELECT * FROM T WHERE k = 3;
-- Output:
+----+-----+----+
| k  | v1  | v2 |
+----+-----+----+
| 3  | 3.0 | t3 |
+----+-----+----+
 
-- Delete
DELETE FROM T WHERE k > 2;
SELECT * FROM T;
-- Output:
+----+-----+----+
| k  | v1  | v2 |
+----+-----+----+
| 1  | 1.0 | t2 |
+----+-----+----+