PolarDB:Limits on database development

UPDATE with ON UPDATE CURRENT_TIMESTAMP

In PolarDB-X, every logical UPDATE sets a column with the ON UPDATE CURRENT_TIMESTAMP attribute to the current timestamp, regardless of whether any other column changed. In MySQL, the column is only updated if at least one other column changes.

Example

-- Create a table with an ON UPDATE CURRENT_TIMESTAMP column
CREATE TABLE t (
  id INT PRIMARY KEY,
  name VARCHAR(50),
  updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

INSERT INTO t VALUES (1, 'Alice', NOW());

-- Update with no actual data change
UPDATE t SET name = 'Alice' WHERE id = 1;

-- PolarDB-X: updated_at is refreshed to CURRENT_TIMESTAMP
-- MySQL:      updated_at is NOT refreshed (no data changed)
SELECT id, name, updated_at FROM t WHERE id = 1;

If your application logic relies on MySQL's behavior of leaving updated_at unchanged when no data changes, update your queries or application code before migrating to PolarDB-X.