问题
I have 3-4 tables in my database which I want to track the changes for.
I am mainly concerned about updates.
Whenever updates happen, I want to store previous entry (value or complete row) in audit table.
Basic columns I was thinking of are as following:
AuditId, TableName, PK1, PK2, PK3, PKVal1, PKVal2, PKVal3, UpdateType, PrevEntryJSON
JSON will be of format: Key:Value and I preferred to go with it as columns keep on changing and I want to keep all values even if they don't change.
Other option is to remove JSON with 100's of columns which will have names same as different columns (cumulative of all tables).
I wanted to hear people's views on this. How could I improve on it and what issues could I face?
Going through triggers might not be preferable way but I am open to it.
Thanks,
回答1:
I have seen a very effective implementation of this which goes as follows:
TABLE audit_entry (
audit_entry_id INTEGER PRIMARY KEY,
audit_entry_type VARCHAR2(10) NOT NULL,
-- ^^ stores 'INSERT' / 'UPDATE' -- / 'DELETE'
table_name VARCHAR2(30) NOT NULL,
-- ^^ stores the name of the table that is changed
column_name VARCHAR2(30) NOT NULL,
-- ^^ stores the name of the column that is changed
primary_key_id INTEGER NOT NULL,
-- ^^ Primary key ID to identify the row that is changed
-- Below are the actual values that are changed.
-- If the changed column is a foreign key ID then
-- below columns tell you which is new and which is old
old_id INTEGER,
new_id INTEGER,
-- If the changed column is of any other numeric type,
-- store the old and new values here.
-- Modify the precision and scale of NUMBER as per your
-- choice.
old_number NUMBER(18,2),
new_number NUMBER(18,2),
-- If the changed column is of date type, with or without
-- time information, store it here.
old_ts TIMESTAMP,
new_ts TIMESTAMP,
-- If the changed column is of VARCHAR2 type,
-- store it here.
old_varchar VARCHAR2(2000),
new_varchar VARCHAR2(2000),
...
... -- Any other columns to store data of other types,
... -- e.g., blob, xmldata, etc.
...
)
And we create a simple sequence to give us new incremental integer value for audit_entry_id:
CREATE SEQUENCE audit_entry_id_seq;
The beauty of a table like audit_entry is that you can store information about all types of DMLs- INSERT, UPDATE and DELETE in the same place.
For e.g., for insert, keep the old_* columns null and populate the new_* with your values.
For updates, populate both old_* and new_* columns whenever they are changed.
For delete, just populate the old_* columns and keep the new_* null.
And of course, enter the appropriate value for audit_entry_type. ;0)
Then, for example, you have a table like follows:
TABLE emp (
empno INTEGER,
ename VARCHAR2(100) NOT NULL,
date_of_birth DATE,
salary NUMBER(18,2) NOT NULL,
deptno INTEGER -- FOREIGN KEY to, say, department
...
... -- Any other columns that you may fancy.
...
)
Just create a trigger on this table as follows:
CREATE OR REPLACE TRIGGER emp_rbiud
-- rbiud means Row level, Before Insert, Update, Delete
BEFORE INSERT OR UPDATE OR DELETE
ON emp
REFERENCING NEW AS NEW OLD AS OLD
DECLARE
-- any variable declarations that deem fit.
BEGIN
WHEN INSERTING THEN
-- Of course, you will insert empno.
-- Let's populate other columns.
-- As emp.ename is a not null column,
-- let's insert the audit entry value directly.
INSERT INTO audit_entry(audit_entry_id,
audit_entry_type,
table_name,
column_name,
primary_key,
new_varchar)
VALUES(audit_entry_id_seq.nextval,
'INSERT',
'EMP',
'ENAME',
:new.empno,
:new.ename);
-- Now, as date_of_birth may contain null, we do:
IF :new.date_of_birth IS NOT NULL THEN
INSERT INTO audit_entry(audit_entry_id,
audit_entry_type,
table_name,
column_name,
primary_key,
new_ts)
VALUES(audit_entry_id_seq.nextval,
'INSERT',
'EMP',
'DATE_OF_BIRTH',
:new.empno,
:new.date_of_birth);
END IF;
-- Similarly, code DML statements for auditing other values
-- as per your requirements.
WHEN UPDATING THEN
-- This is a tricky one.
-- You must check which columns have been updated before you
-- hurry into auditing their information.
IF :old.ename != :new.ename THEN
INSERT INTO audit_entry(audit_entry_id,
audit_entry_type,
table_name,
column_name,
primary_key,
old_varchar,
new_varchar)
VALUES(audit_entry_id_seq.nextval,
'INSERT',
'EMP',
'ENAME',
:new.empno,
:old.ename,
:new.ename);
END IF;
-- Code further DML statements in similar fashion for other
-- columns as per your requirement.
WHEN DELETING THEN
-- By now you must have got the idea about how to go about this.
-- ;0)
END;
/
Just one word of caution: be selective with what tables and columns you choose to audit, because anyways, you this table will have a huge number of rows. SELECT statements on this table will be slower than you may expect.
I would really love to see any other sort of implementation here, as it would be a good learning experience. Hope your question gets more answers, as this is the best implementation of an audit table that I have seen and I'm still looking for ways to make it better.
来源：https://stackoverflow.com/questions/21180401/audit-history-of-multiple-tables-in-the-database