How to modify table records in oracle

Oracle database is currently the most widely used relational database management system in the world. It has rich functions and flexible configuration. In Oracle database, tables are an important part of data storage. The structure of the table includes column names, column types, constraints, etc. Modifying the table structure is a common data operation, but the modification operation may have a certain impact on the integrity and security of the data. Therefore, special attention needs to be paid when modifying the table structure.

In order to record the modification process of the table structure and ensure the integrity and traceability of the data, Oracle database provides a variety of methods to record table modifications. This article will introduce the following methods of modifying the record table.

1. Oracle Flashback Table
   Oracle Flashback Table is an advanced feature of Oracle that can restore the historical state of a table or undo data changes at a specific point in time. Before using Flashback Table, you need to enable Oracle logs to record modifications to the table. When performing an update or delete operation, the system will record the data before modification to the undo table space. Flashback Table can use this undo information to roll back the state of the table to the same state as before modification.

Flashback Table was launched in the Oracle10g version, and it requires SYSTEM permissions to execute. Before executing Flashback Table, you can use the following statement to query which tables have logging enabled in the database:

SELECT LOG_MODE FROM V$DATABASE;

If the query result is "ARCHIVELOG", it means that the database has logging enabled.

When using Flashback Table, you need to pay attention to the following points:

• Flashback Table can only restore update and delete operations, but cannot restore table structure modifications.
• Flashback Table uses undo table space. If the undo table space is insufficient, the modification history cannot be recorded.
• Flashback Table cannot recover data that has been deleted by the truncate command because this command will clear the undo table space.

2. Oracle Trigger
   Oracle Trigger triggers specified actions before and after a table is inserted, updated, or deleted. You can create a Trigger to record the history of table operations. By creating before insert, before update, and before delete triggers on the table, the data before modification is recorded. In after insert, after update, and after delete trigger, the modified data is recorded.

The following is an example of a Trigger that records the modification history of the student table:

CREATE TABLE STUDENT_HISTORY (
    ID INT PRIMARY KEY,
    OPERATION_TYPE VARCHAR(10) NOT NULL,
    OPERATE_TIME DATE NOT NULL,
    NAME VARCHAR2(50) NOT NULL,
    AGE INT NOT NULL,
    SEX VARCHAR2(10) NOT NULL,
    GRADE VARCHAR2(20) NOT NULL,
    REMARKS VARCHAR2(100)
);

CREATE OR REPLACE TRIGGER STUDENT_HISTORY_TRG
BEFORE DELETE OR UPDATE OR INSERT ON STUDENT
FOR EACH ROW
BEGIN
    IF DELETING THEN
        INSERT INTO STUDENT_HISTORY (ID, OPERATION_TYPE, OPERATE_TIME, NAME, AGE, SEX, GRADE, REMARKS)
        VALUES (:OLD.ID, 'DELETE', SYSDATE, :OLD.NAME, :OLD.AGE, :OLD.SEX, :OLD.GRADE, :OLD.REMARKS);
    ELSIF UPDATING THEN
        INSERT INTO STUDENT_HISTORY (ID, OPERATION_TYPE, OPERATE_TIME, NAME, AGE, SEX, GRADE, REMARKS)
        VALUES (:OLD.ID, 'UPDATE', SYSDATE, :NEW.NAME, :NEW.AGE, :NEW.SEX, :NEW.GRADE, :NEW.REMARKS);
    ELSIF INSERTING THEN
        INSERT INTO STUDENT_HISTORY (ID, OPERATION_TYPE, OPERATE_TIME, NAME, AGE, SEX, GRADE, REMARKS)
        VALUES (:NEW.ID, 'INSERT', SYSDATE, :NEW.NAME, :NEW.AGE, :NEW.SEX, :NEW.GRADE, :NEW.REMARKS);
    END IF;
END;

This Trigger records the modification history of the student table into the STUDENT_HISTORY table. When performing insert, update, and delete operations, Trigger will record the operation type, operation time, student name, age, gender, grade, and remarks.

The advantages of using Trigger to record modification history are:

• Trigger can record modifications to the table structure, as well as insert, update, delete and other operations;
• Trigger can record The data before and after modification can be traced back to the data change process;
• Trigger can customize the content and method of recording, which is highly flexible.

However, there are also some disadvantages to using Trigger:

• Trigger will affect database performance;
• Need to write complex PL/SQL code, if the code Problems may affect data integrity.

3. Oracle AUDIT
   Oracle AUDIT is a database-level audit function that can record the history of database user operations. The AUDIT feature includes a global audit trailer and multiple policy options. Users can control logging behavior by setting policy options. AUDIT is already built into the Oracle database and requires no additional installation.

The following is an AUDIT policy that records the user's insert, update, and delete operations on the EMPLOYEES table:

AUDIT INSERT, UPDATE, DELETE ON EMPLOYEES BY SESSION;

This statement will record the user's insert, update, and delete operations on the EMPLOYEES table. BY SESSION means recording the operation performed by which session. You can use the following statement to check the enabled status of Audit:

SELECT * FROM DBA_OBJ_AUDIT_OPTS WHERE OWNER='HR' AND OBJ_NAME='EMPLOYEES';

The advantage of using AUDIT to record table modification history is:

• Audit can record the global user operation history of the database, including table structure modifications , insert, update, delete and other operations;
• can easily extract and analyze audit data;
• No need to write additional code.

However, AUDIT also has some limitations:

• AUDIT is implemented at the database level, so it cannot record the execution process of SQL statements;
• AUDIT is useful for recording The data format is limited and not flexible enough;
• AUDIT will have a certain impact on database performance.

4. Oracle Database Change Management Pack
   Oracle Database Change Management Pack is a pluggable database management tool that can manage and audit database changes. Database Change Management Pack generates and stores high-quality change documentation, audit trail information, and change reports.

Database Change Management Pack allows users to have a complete picture of the database change status, including:

• The change history of database objects;
• The identity of the person who modified it and the time and date of the operation;
• A changed document and artifact.

In the Database Change Management Pack, users can specify the objects and policy options that need to be audited and generate change tracking data. It can also automatically generate change documentation and artifacts and conduct audits after each database change.

The advantages of using Database Change Management Pack are:

• Database Change Management Pack can record all database changes, including DDL operations and data modifications;
• can generate changes Documents and audit reports facilitate security audits and problem troubleshooting;
• can automatically detect the standardization and completeness of database changes.

However, Database Change Management Pack also has some disadvantages:

• It requires additional purchase and the cost is high;
• It requires a certain amount of time and energy to carry out. Configuration and management.

Summary:
Oracle is currently the most widely used database in the world. It provides a variety of methods for recording table modification history, including Flashback Table, Trigger, AUDIT and Database Change Management Pack. Each of these methods has advantages and disadvantages, and users need to choose and use them according to specific circumstances.

When modifying the table structure, you must be extremely careful to avoid affecting the integrity and security of the data. If important data is saved in the database, it is recommended to back up the data before modifying it. Timely recording of table modification history and conducting audits are very effective in ensuring data integrity and security.

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