How to create Triggers to add the change events into Audit Log tables

Question

Suppose we have 50 tables in a database and we want to capture all the changes (Previous value and new value of columns) across the columns of each table. An audit table will be there, which will have below columns:

ID, Server_Name, User_Name, Date_Time, Table_Name, Column_Name, Old_Value, New_Value

There will be one audit table which will capture the changes of all the tables from that database. I believe we can create triggers for each of the table of that database. But please let me know how all the data will be added into one audit table. If you can provide me with a working example that will be very helpful.

Thanks and regards, Partha

Answer 1

I can provide you a kind of algorithm to work upon, most of the ground work is already done:

This can be your audit table, should add timestamp column as modified date or more info as per your requirements:

CREATE TABLE audit (
     old_data VARCHAR(100),
     new_data VARCHAR(100),
     tbl_name VARCHAR(100)
)
|

This can be used as a reference trigger; note that there will be a separate trigger for each table:

CREATE TRIGGER testtrigger BEFORE UPDATE ON <table_name>
  FOR EACH ROW BEGIN
    INSERT INTO audit(old_data, new_data, tbl_name) VALUES (OLD.first_name, NEW.first_name, "testtable");
  END;
|

You can have multiple insert statement one for each column. If you want to put a restriction of not inserting the data that is not changed you can do the following change in the trigger:

IF(OLD.column_name <> NEW.column_name) THEN
    --Your insert query here
ELSE
    --NOOP
END IF;

Let know if more information is required.

Answer 2

you can use this trigger but if it is for each table for me it is the best because you control if something changes in the structure of the table and does not affect the others, you can use the example of this repo: https://github.com/areliszxz/mysql_audit

DELIMITER $$
USE `tudbaauditar`$$
CREATE
TRIGGER `tudbaauditar`.`update`
BEFORE UPDATE ON `tudbaauditar`.`tutablaaauditar` #aqui puedes poner antes o despues del update
FOR EACH ROW
BEGIN
        /*Paso de variables para un mejor control*/
        set @res1 = ''; set @res2 = ''; set @res3 = ''; set @res4 = '';
        /*Sacamos info de la ip donde se ejecuta la accion de UPDATE*/
        select host as IP INTO @ipcl from information_schema.processlist WHERE ID=connection_id();
        #concatenamos los campos de la tabla a auditar y verificamos que no sean null, en caso de que los campos sean null agregamos un espacio
        #las variables (new,old)son de mysql, el valor old es el que ya se tenia en la tabla y el new es el valor que se modifico

        #Valores viejos
        SET @oldq = CONCAT (' id ',ifnull(OLD.id,''),
                                                        ' campo1 ',ifnull(OLD.campo1,''),
                                                        ' campo2 ',ifnull(OLD.campo2,''),
                                                        ' campo3 ',ifnull(OLD.campo3,''));
        #Valores nuevos
        SET @newq = CONCAT (' id ',ifnull(new.id,''),
                                                        ' campo1 ',ifnull(new.campo1,''),
                                                        ' campo2 ',ifnull(new.campo2,''),
                                                        ' campo3 ',ifnull(new.campo3,''));
    #guardamos en una variable los valores que unicamente cambiaron                                                 
    IF OLD.id <> new.id THEN set @res1 = CONCAT ('Cambio id ',ifnull(OLD.id,''), ' a: ',ifnull(new.id,'')); END IF;
    IF OLD.campo1 <> new.campo1 THEN set @res2 = CONCAT ('Cambio campo1 ',ifnull(OLD.campo1,''), ' a: ',ifnull(new.campo1,'')); END IF;
    IF OLD.campo2 <> new.campo2 THEN set @res3 = CONCAT ('Cambio campo2 ',ifnull(OLD.campo2,''), ' a: ',ifnull(new.campo2,'')); END IF;
    IF OLD.campo3 <> new.campo3 THEN set @res4 = CONCAT ('Cambio campo3 ',ifnull(OLD.campo3,''), ' a: ',ifnull(new.campo3,'')); END IF;
    SET @resC=CONCAT(ifnull(@res1,''),'|',ifnull(@res2,''),'|',ifnull(@res3,''),'|',ifnull(@res4,''));

    #insertamos en nuestra tabla de log la informacion
    INSERT INTO basedeauditoria.tablalogs (old,new,usuario,typo,fecha,tabla,valor_alterado,ip)                
    VALUES (@oldq ,@newq,CURRENT_USER,"UPDATE",NOW(),"tutablaaauditar",ifnull(@resC,'No cambio nada'),@ipcl);
END$$

#log de insertados(Nuevos registros)
DELIMITER $$
USE `tudbaauditar`$$
CREATE
TRIGGER `tudbaauditar`.`incert`
BEFORE INSERT ON `tudbaauditar`.`tutablaaauditar`
FOR EACH ROW
BEGIN
    SET @oldq = '';
    SET @newq = CONCAT (' id ',ifnull(new.id,''),
    ' campo1 ',ifnull(new.campo1,''),
    ' campo2 ',ifnull(new.campo2,''),
    ' campo3 ',ifnull(new.campo3,''));
    INSERT INTO sys_logdev.logs (old,new,usuario,typo,fecha,tabla)                
    VALUES (@oldq ,@newq,CURRENT_USER,"INSERT",NOW(),"tutablaaauditar");
END$$

#log de Borrados
DELIMITER $$
USE `tudbaauditar`$$
CREATE
TRIGGER `tudbaauditar`.`delete`
AFTER DELETE ON `tudbaauditar`.`tutablaaauditar`
FOR EACH ROW
BEGIN
    SET @newq = '';
    SET @oldq = CONCAT (' id ',ifnull(new.id,''),
    ' campo1 ',ifnull(new.campo1,''),
    ' campo2 ',ifnull(new.campo2,''),
    ' campo3 ',ifnull(new.campo3,''));
    INSERT INTO sys_logdev.logs (old,new,usuario,typo,fecha,tabla)                
    VALUES (@oldq ,@newq,CURRENT_USER,"DELETE",NOW(),"tutablaaauditar");
END$$

Answer 3

This is a little bit improved version of Vlad answer. Audit table has column for 'diff' of changes.

Auditing rules:

• INSERT and DELETE - complete record with all fields is stored to audit table
• UPDATE - only changes on fields is stored

Audit table structure. diff is column where changes are stored.

NB: privileges is JSON column on table we are auditing in this case.

CREATE TABLE roles_audit_log (
    roles_id INT UNSIGNED NOT NULL,
    diff JSON,
    dml_type ENUM('INSERT', 'UPDATE', 'DELETE') NOT NULL,
    dml_timestamp TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    dml_created_by VARCHAR(255) NOT NULL default 'system',
    PRIMARY KEY (roles_id, dml_type, dml_timestamp)
);

Trigger for UPDATE statement. Will fill diff column with fields that were changed.

DELIMITER $$

CREATE TRIGGER roles_audit_au AFTER UPDATE ON `roles` FOR EACH ROW
BEGIN
    DECLARE m_change text;
    SET m_change = JSON_OBJECT();

    IF coalesce(NEW.role, '') != coalesce(OLD.role, '') THEN
        SET m_change = JSON_SET(m_change, '$.role', NEW.role);
    END IF;

    IF coalesce(NEW.created_at, '') != coalesce(OLD.created_at, '') THEN
        SET m_change = JSON_SET(m_change, '$.created_at', NEW.created_at);
    END IF;

    IF coalesce(NEW.updated_at, '') != coalesce(OLD.updated_at, '') THEN
        SET m_change = JSON_SET(m_change, '$.updated_at', NEW.updated_at);
    END IF;

    IF coalesce(NEW.privileges, '') != coalesce(OLD.privileges, '') THEN
        SET m_change = JSON_SET(m_change, '$.privileges', NEW.privileges);
    END IF;

    INSERT INTO `roles_audit_log` (
        roles_id,
        diff,
        dml_type,
        dml_created_by
    ) VALUES(
        NEW.id,
        m_change,
        'UPDATE',
        coalesce(@logged_user, 'system')
    );
END;$$
DELIMITER ;

Trigger for DELETE statement. Will fill diff with complete row that was deleted.

DELIMITER $$

CREATE TRIGGER roles_audit_ad AFTER DELETE ON `roles` FOR EACH ROW
BEGIN
    INSERT INTO `roles_audit_log` (
        roles_id,
        diff,
        dml_type,
        dml_created_by
    ) VALUES(
        OLD.id,
        JSON_OBJECT(
            'id', OLD.id,
            'role', OLD.role,
            'privileges', OLD.privileges,
            'created_at', OLD.created_at,
            'updated_at', OLD.updated_at
        ),
        'DELETE',
        coalesce(@logged_user, 'system')
    );
END;$$
DELIMITER ;

Trigger for INSERT statement. Will fill diff with complete row that was deleted.

DELIMITER $$

CREATE TRIGGER roles_audit_ai AFTER INSERT ON `roles` FOR EACH ROW
BEGIN
    INSERT INTO `roles_audit_log` (
        roles_id,
        diff,
        dml_type,
        dml_created_by
    ) VALUES(
        NEW.id,
        JSON_OBJECT(
            'id', NEW.id,
            'role', NEW.role,
            'privileges', NEW.privileges,
            'created_at', NEW.created_at,
            'updated_at', NEW.updated_at
        ),
        'INSERT',
        coalesce(@logged_user, 'system')
    );
END;$$
DELIMITER ;

Answer 4

I have spent a few days to come up with a Stored Procedure to automatically/dynamically create UPDATE / DELETE triggers in MariaDB (Works with v 10.1.9) auditing all changes on updates and deletions. The solution uses the INFORMATION_SCHEMA to automatically build an audit trigger for each of your tables. On Update only changed columns are audited, whilst on delete all the history is retained in the audit.

In the example below we create a test database with two tables, tb_company and tb_auditdetail which will hold our audit log.

    -- Dynamic Automated Update / Delete Triggers in MariaDB
    -- Leonard Tonna 19/05/2016 - www.ilabmalta.com

    CREATE DATABASE db_ilabmalta_test;

    USE db_ilabmalta_test;

    CREATE TABLE tb_auditDetail(
        audit_pk int(9) NOT NULL PRIMARY KEY AUTO_INCREMENT,
        type varchar(1) NOT NULL,
        tablename varchar(128) NULL,
        pk varchar(128) NULL,
        fieldname varchar(128) NULL,
        oldvalue varchar(1000) NULL,
        newvalue varchar(1000) NULL,
        updatedate datetime NULL,
        username varchar(128) NULL,
        dbusername varchar(128) NULL,
        machinename varchar(128) NULL);

    CREATE TABLE tb_company(
        cmp_pk int(9) NOT NULL PRIMARY KEY AUTO_INCREMENT,
        cmp_name varchar(100) NOT NULL,
        cmp_no varchar(16) NULL,
        cmp_status smallint NOT NULL DEFAULT 1,
        cmp_created datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
        cmp_createdby varchar(10) NOT NULL,
        cmp_updated datetime NULL,
        cmp_updatedby varchar(10) NULL,
        cmp_record_version int(9) NOT NULL DEFAULT 1 ) ;

    -- We now create sp_maketrigger which is the stored procedure
    -- which will give us our trigger scripts

    DELIMITER $$

    DROP PROCEDURE IF EXISTS sp_maketrigger; 

    CREATE PROCEDURE sp_maketrigger (IN s_tablename CHAR(30), OUT u_trigger_out VARCHAR(65500) CHARACTER SET ascii,OUT d_trigger_out VARCHAR(65500) CHARACTER SET ascii)
    BEGIN
        DECLARE s_fieldname VARCHAR(50);
        DECLARE u_trigger VARCHAR(65500) CHARACTER SET ascii;
        DECLARE d_trigger VARCHAR(65500) CHARACTER SET ascii;
        DECLARE s_key VARCHAR(50);
        DECLARE s_updatedby VARCHAR(50);
        DECLARE s_updated VARCHAR(50);
        DECLARE s_recversion VARCHAR(50);
        DECLARE done INT DEFAULT 0; 
        DECLARE cursor_end CONDITION FOR SQLSTATE '02000'; 
        DECLARE col_cursor CURSOR FOR SELECT COLUMN_NAME FROM test_prepare_vw;
        DECLARE pri_cursor CURSOR FOR SELECT COLUMN_NAME FROM test_prepare_vw2;
        DECLARE upd_cursor CURSOR FOR SELECT COLUMN_NAME FROM test_prepare_vw3;
        DECLARE rec_cursor CURSOR FOR SELECT COLUMN_NAME FROM test_prepare_vw4;
        DECLARE CONTINUE HANDLER FOR cursor_end SET done = 1; 

        DROP VIEW IF EXISTS test_prepare_vw; 
        DROP VIEW IF EXISTS test_prepare_vw2; 
        DROP VIEW IF EXISTS test_prepare_vw3; 
        DROP VIEW IF EXISTS test_prepare_vw4; 

        SET u_trigger = '';
        SET u_trigger = CONCAT('DELIMITER $$ \nDROP TRIGGER IF EXISTS tra_',s_tablename,'_update;\n');
        SET u_trigger = CONCAT(u_trigger,'CREATE TRIGGER tra_',s_tablename,'_update AFTER UPDATE ON ',s_tablename,' FOR EACH ROW \n');
        SET u_trigger = CONCAT(u_trigger,'BEGIN \n');
        SET u_trigger = CONCAT(u_trigger,'DECLARE msg VARCHAR(255); \n');

        SET d_trigger = '';
        SET d_trigger = CONCAT('DELIMITER $$ \nDROP TRIGGER IF EXISTS tra_',s_tablename,'_delete;\n');
        SET d_trigger = CONCAT(d_trigger,'CREATE TRIGGER tra_',s_tablename,'_delete AFTER DELETE ON ',s_tablename,' FOR EACH ROW \n');
        SET d_trigger = CONCAT(d_trigger,'BEGIN \n');

        SET @query = CONCAT('CREATE VIEW test_prepare_vw2 as SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name = \'', s_tablename, '\' AND table_schema = \'db_diers\' AND COLUMN_NAME NOT LIKE \'%updated%\' AND COLUMN_KEY = \'PRI\' ORDER BY ORDINAL_POSITION'); 
        PREPARE stmt from @query; 
        EXECUTE stmt; 
        DEALLOCATE PREPARE stmt; 

        OPEN pri_cursor;
        FETCH pri_cursor INTO s_key; 
        CLOSE pri_cursor; 
        DROP VIEW test_prepare_vw2; 

        SET @query = CONCAT('CREATE VIEW test_prepare_vw3 as SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name = \'', s_tablename, '\' AND table_schema = \'db_diers\' AND COLUMN_NAME LIKE \'%updatedby%\' AND COLUMN_KEY <> \'PRI\' ORDER BY ORDINAL_POSITION'); 
        PREPARE stmt from @query; 
        EXECUTE stmt; 
        DEALLOCATE PREPARE stmt; 

        OPEN upd_cursor;
        FETCH upd_cursor INTO s_updatedby; 
        CLOSE upd_cursor; 
        DROP VIEW test_prepare_vw3; 
        SET s_updated = LEFT(s_updatedby,(LENGTH(RTRIM(s_updatedby)))-2);

        SET @query = CONCAT('CREATE VIEW test_prepare_vw4 as SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name = \'', s_tablename, '\' AND table_schema = \'db_diers\' AND COLUMN_NAME LIKE \'%record_version%\' AND COLUMN_KEY <> \'PRI\' ORDER BY ORDINAL_POSITION'); 
        PREPARE stmt from @query; 
        EXECUTE stmt; 
        DEALLOCATE PREPARE stmt; 

        OPEN rec_cursor;
        FETCH rec_cursor INTO s_recversion; 
        CLOSE rec_cursor; 
        DROP VIEW test_prepare_vw4; 

        SET @query = CONCAT('CREATE VIEW test_prepare_vw as SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name = \'', s_tablename, '\' AND table_schema = \'db_diers\' AND COLUMN_KEY <> \'PRI\' ORDER BY ORDINAL_POSITION'); 
        PREPARE stmt from @query; 
        EXECUTE stmt; 
        DEALLOCATE PREPARE stmt; 

        SET u_trigger = CONCAT(u_trigger,'   IF (ISNULL(NEW.',s_recversion,') OR OLD.',s_recversion,' >= NEW.',s_recversion,' OR ISNULL(NEW.',s_updatedby,') OR NEW.',s_updatedby,' = \'\' OR ISNULL(NEW.',s_updated,') OR NEW.',s_updated,' = OLD.',s_updated,') THEN \n');
        SET u_trigger = CONCAT(u_trigger,'      set msg = \'Cannot update record without specifying updated/updatedby by columns and without incrementing the record version.\'; \n');
        SET u_trigger = CONCAT(u_trigger,'      SIGNAL SQLSTATE \'45000\' SET MESSAGE_TEXT = msg; \n');
        SET u_trigger = CONCAT(u_trigger,'   END IF;     \n');

        OPEN col_cursor;

        FETCH col_cursor INTO s_fieldname; 
        WHILE done = 0 DO 
            SET u_trigger = CONCAT(u_trigger,'   IF (IFNULL(OLD.',s_fieldname,',\'\') <> IFNULL(NEW.',s_fieldname,',\'\') ) THEN\n');
            SET u_trigger = CONCAT(u_trigger,'     INSERT INTO tb_auditdetail (type, tablename, pk, fieldname, oldvalue, newvalue, updatedate, username, dbusername, machinename) \n');
            SET u_trigger = CONCAT(u_trigger,'     VALUES (\'U\', \'',s_tablename,'\', OLD.',s_key,', \'',s_fieldname,'\', OLD.',s_fieldname,', NEW.',s_fieldname,', CURRENT_TIMESTAMP,NEW.',s_updatedby,',CURRENT_USER(),@@hostname);\n');
            SET u_trigger = CONCAT(u_trigger,'   END IF;\n'); 

            SET d_trigger = CONCAT(d_trigger,'     INSERT INTO tb_auditdetail (type, tablename, pk, fieldname, oldvalue, newvalue, updatedate, username, dbusername, machinename) \n');
            SET d_trigger = CONCAT(d_trigger,'     VALUES (\'D\', \'',s_tablename,'\', OLD.',s_key,', \'',s_fieldname,'\', OLD.',s_fieldname,',NULL, CURRENT_TIMESTAMP,NULL,CURRENT_USER(),@@hostname);\n');

            FETCH col_cursor INTO s_fieldname; 
        END WHILE; 
        CLOSE col_cursor; 

        DROP VIEW test_prepare_vw; 

        SET u_trigger = CONCAT(u_trigger,'END;$$ \nDELIMITER ; \n');
        SET d_trigger = CONCAT(d_trigger,'END;$$ \nDELIMITER ; \n');
        SELECT u_trigger INTO u_trigger_out;
        SELECT d_trigger INTO d_trigger_out;


    END; $$

    DELIMITER ;

    -- And finally, to extract the Trigger Scripts

    call sp_maketrigger('tb_company',@s_line1,@d_line1);

    SELECT CONCAT(@s_line1,@d_line1)

    -- You just need to copy, paste and execute the trigger script, and
    -- voila, your audit is in place.

The above example takes it for granted that with each of your tables you have 5 columns: created, createdby, updated, updatedby, record_version.

However you can customise the Stored Procedure sp_maketrigger differently to suit your needs. The sp is also subject to enhancements and improvements.

Answer 5

Database tables

Let's assume we have a library application that has the following two tables:

The best way to store the old and new row state is to use JSON columns. So, for each table that you want to enable audit logging, you can create an audit log table, like this one:

CREATE TABLE book_audit_log (
    book_id BIGINT NOT NULL, 
    old_row_data JSON,
    new_row_data JSON,
    dml_type ENUM('INSERT', 'UPDATE', 'DELETE') NOT NULL,
    dml_timestamp TIMESTAMP NOT NULL,
    dml_created_by VARCHAR(255) NOT NULL,
    PRIMARY KEY (book_id, dml_type, dml_timestamp)
)

• The book_id column stores the identifier of the book row that has been either created, updated, or deleted.
• The old_row_data is a JSON column that will capture the state of the book record prior to executing an INSERT, UPDATE, or DELETE statement.
• The new_row_data is a JSON column that will capture the state of the book record after executing an INSERT, UPDATE, or DELETE statement.
• The dml_type is an enumeration column that stores the DML statement type that created, updated, or deleted a given book record.
• The dml_timestamp stores the DML statement execution timestamp.
• The dml_created_by stores the application user who issued the INSERT, UPDATE, or DELETE DML statement.

Intercepting INSERT, UPDATE, and DELETE DML statements using triggers

Now, to feed the audit log tables, you need to create the following 3 triggers:

CREATE TRIGGER book_insert_audit_trigger
AFTER INSERT ON book FOR EACH ROW 
BEGIN
    INSERT INTO book_audit_log (
        book_id,
        old_row_data,
        new_row_data,
        dml_type,
        dml_timestamp,
        dml_created_by
    )
    VALUES(
        NEW.id,
        null,
        JSON_OBJECT(
            "title", NEW.title,
            "author", NEW.author,
            "price_in_cents", NEW.price_in_cents,
            "publisher", NEW.publisher
        ),
        'INSERT',
        CURRENT_TIMESTAMP,
        @logged_user
    );
END

CREATE TRIGGER book_update_audit_trigger
AFTER UPDATE ON book FOR EACH ROW 
BEGIN
    INSERT INTO book_audit_log (
        book_id,
        old_row_data,
        new_row_data,
        dml_type,
        dml_timestamp,
        dml_created_by
    )
    VALUES(
        NEW.id,
        JSON_OBJECT(
            "title", OLD.title,
            "author", OLD.author,
            "price_in_cents", OLD.price_in_cents,
            "publisher", OLD.publisher
        ),
        JSON_OBJECT(
            "title", NEW.title,
            "author", NEW.author,
            "price_in_cents", NEW.price_in_cents,
            "publisher", NEW.publisher
        ),
        'UPDATE',
        CURRENT_TIMESTAMP,
        @logged_user
    );
END

CREATE TRIGGER book_delete_audit_trigger
AFTER DELETE ON book FOR EACH ROW 
BEGIN
    INSERT INTO book_audit_log (
        book_id,
        old_row_data,
        new_row_data,
        dml_type,
        dml_timestamp,
        dml_created_by
    )
    VALUES(
        OLD.id,
        JSON_OBJECT(
            "title", OLD.title,
            "author", OLD.author,
            "price_in_cents", OLD.price_in_cents,
            "publisher", OLD.publisher
        ),
        null,
        'DELETE',
        CURRENT_TIMESTAMP,
        @logged_user
    );
END

The JSON_OBJECT MySQL function allows us to create a JSON object that takes the provided key-value pairs.

The dml_type column is set to the value of INSERT, UPDATE or DELETE and the dml_timestamp value is set to the CURRENT_TIMESTAMP.

The dml_created_by column is set to the value of the @logged_user MySQL session variable, which was previously set by the application with the currently logged user:

Session session = entityManager.unwrap(Session.class);

Dialect dialect = session.getSessionFactory()
    .unwrap(SessionFactoryImplementor.class)
    .getJdbcServices()
    .getDialect();

session.doWork(connection -> {
    update(
        connection,
        String.format(
            "SET @logged_user = '%s'", 
            ReflectionUtils.invokeMethod(
                dialect,
                "escapeLiteral",
                LoggedUser.get()
            )
        )
    );
});

Testing time

When executing an INSERT statement on the book table:

INSERT INTO book (
    id,
    author, 
    price_in_cents, 
    publisher, 
    title
) 
VALUES (
    1,
    'Vlad Mihalcea', 
    3990, 
    'Amazon', 
    'High-Performance Java Persistence 1st edition'
)

We can see that a record is inserted in the book_audit_log that captures the INSERT statement that was just executed on the book table:

| book_id | old_row_data | new_row_data                                                                                                                         | dml_type | dml_timestamp       | dml_created_by |
|---------|--------------|--------------------------------------------------------------------------------------------------------------------------------------|----------|---------------------|----------------|
| 1       |              | {"title": "High-Performance Java Persistence 1st edition", "author": "Vlad Mihalcea", "publisher": "Amazon", "price_in_cents": 3990} | INSERT   | 2020-07-29 13:40:15 | Vlad Mihalcea  |

When updating the book table row:

UPDATE book 
SET price_in_cents = 4499 
WHERE id = 1

We can see that a new record is going to be added to the book_audit_log by the AFTER UPDATE trigger on the book table:

| book_id | old_row_data                                                                                                                         | new_row_data                                                                                                                         | dml_type | dml_timestamp       | dml_created_by |
|---------|--------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------|----------|---------------------|----------------|
| 1       |                                                                                                                                      | {"title": "High-Performance Java Persistence 1st edition", "author": "Vlad Mihalcea", "publisher": "Amazon", "price_in_cents": 3990} | INSERT   | 2020-07-29 13:40:15 | Vlad Mihalcea  |
| 1       | {"title": "High-Performance Java Persistence 1st edition", "author": "Vlad Mihalcea", "publisher": "Amazon", "price_in_cents": 3990} | {"title": "High-Performance Java Persistence 1st edition", "author": "Vlad Mihalcea", "publisher": "Amazon", "price_in_cents": 4499} | UPDATE   | 2020-07-29 13:50:48 | Vlad Mihalcea  |

When deleting the book table row:

DELETE FROM book 
WHERE id = 1

A new record is added to the book_audit_log by the AFTER DELETE trigger on the book table:

| book_id | old_row_data                                                                                                                         | new_row_data                                                                                                                         | dml_type | dml_timestamp       | dml_created_by |
|---------|--------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------|----------|---------------------|----------------|
| 1       |                                                                                                                                      | {"title": "High-Performance Java Persistence 1st edition", "author": "Vlad Mihalcea", "publisher": "Amazon", "price_in_cents": 3990} | INSERT   | 2020-07-29 13:40:15 | Vlad Mihalcea  |
| 1       | {"title": "High-Performance Java Persistence 1st edition", "author": "Vlad Mihalcea", "publisher": "Amazon", "price_in_cents": 3990} | {"title": "High-Performance Java Persistence 1st edition", "author": "Vlad Mihalcea", "publisher": "Amazon", "price_in_cents": 4499} | UPDATE   | 2020-07-29 13:50:48 | Vlad Mihalcea  |
| 1       | {"title": "High-Performance Java Persistence 1st edition", "author": "Vlad Mihalcea", "publisher": "Amazon", "price_in_cents": 4499} |                                                                                                                                      | DELETE   | 2020-07-29 14:05:33 | Vlad Mihalcea  |

That's it!