The spi module provides several workable examples of using the Server Programming Interface (SPI) and triggers.

YugabyteDB supports the following four (of five — timetravel is not currently supported) extensions provided in the spi module:

• autoinc functions auto-increment fields.
• insert_username functions track who changed a table.
• moddatetime functions track last modification times.
• refint functions implement referential integrity.

Example

1. Connect using ysqlsh and run the following commands:

   CREATE EXTENSION insert_username;
   CREATE EXTENSION moddatetime;
   

2. Set up a table with triggers for tracking modification time and user (role):

   CREATE TABLE spi_test (
     id int primary key,
     content text,
     username text not null,
     moddate timestamp DEFAULT CURRENT_TIMESTAMP NOT NULL
   );
   
   CREATE TRIGGER insert_usernames
     BEFORE INSERT OR UPDATE ON spi_test
     FOR EACH ROW
     EXECUTE PROCEDURE insert_username (username);
   
   CREATE TRIGGER update_moddatetime
     BEFORE UPDATE ON spi_test
     FOR EACH ROW
     EXECUTE PROCEDURE moddatetime (moddate);
   

3. Insert some rows. Each insert should add the current role as username and the current timestamp as moddate.

   SET ROLE yugabyte;
   INSERT INTO spi_test VALUES(1, 'desc1');
   
   SET ROLE postgres;
   INSERT INTO spi_test VALUES(2, 'desc2');
   INSERT INTO spi_test VALUES(3, 'desc3');
   
   SET ROLE yugabyte;
   INSERT INTO spi_test VALUES(4, 'desc4');
   
   SELECT * FROM spi_test ORDER BY id;
   

    id | content | username |          moddate
   ----+---------+----------+----------------------------
     1 | desc1   | yugabyte | 2019-09-13 16:55:53.969907
     2 | desc2   | postgres | 2019-09-13 16:55:53.983306
     3 | desc3   | postgres | 2019-09-13 16:55:53.98658
     4 | desc4   | yugabyte | 2019-09-13 16:55:53.991315
   (4 rows)
   

   The yugabyte and (for compatibility) postgres YSQL users are created by default.

4. Update some rows. This should update both username and moddate accordingly.

   UPDATE spi_test SET content = 'desc1_updated' WHERE id = 1;
   UPDATE spi_test SET content = 'desc3_updated' WHERE id = 3;
   
   SELECT * FROM spi_test ORDER BY id;
   

   id |    content    | username |          moddate
   ----+---------------+----------+----------------------------
     1 | desc1_updated | yugabyte | 2019-09-13 16:56:27.623513
     2 | desc2         | postgres | 2019-09-13 16:55:53.983306
     3 | desc3_updated | yugabyte | 2019-09-13 16:56:27.634099
     4 | desc4         | yugabyte | 2019-09-13 16:55:53.991315
   (4 rows)