I have a MySQL table myTable with 4 columns id,name,version and date. Everyday I get the data and this data changes only when they install new version of our products.
I would like to analyze the change in version numbers over time, to analyze when and how many customers are installing this new version.
For example,
INSERT INTO MYtABLE (ID,NAME,VERSION,DATE) VALUES (1, 'ABC','1.0','07/21/2016');
INSERT INTO MYtABLE (ID,NAME,VERSION,DATE) VALUES (1, 'ABC','1.0','07/22/2016');
INSERT INTO MYtABLE (ID,NAME,VERSION,DATE) VALUES (1, 'ABC','1.1','07/23/2016');
In this case, because of change in version from 1.0 to 1.1 I would like to capture the name, id, date of 07/23/2016.
Here is my question:
How do i implement this in MySQL?
to implement Change Data Capture? I'm new to this and I couldn't find any tutorials as well.
I can think of Creating a trigger which captures this change. But it involves performance overhead.
Or a SELECT will work here?
Any better solns?
I can bear the performance! So upon insert, how do we compare the values to capture this change? Or How do I track these changes?
Trigger is the best solution here.
There is another solution that you can schedule a script that run on every minutes or every 5 minutes and capture the data change.
Related
We're using MariaDb in production and we've added a MariaDb slave so that our data team can perform some ETL tasks from this slave to our datawarehouse. However, they lack a proper Change Data Capture feature (i.e. they want to know which rows from the production table changed since yesterday in order to query rows that actually changed).
I saw that MariaDb's 10.3 had an interesting feature that allowed to perform a SELECT on an older version of a table. However, I haven't found resources that supported the idea that it could be used for CDC, any feedback on this feature?
If not, we'll probably resort to streaming the slave's binlogs to our datawarehouse but that looks challenging..
Thanks for your help!
(As a supplement to Stefans answer)
Yes, the System-Versioning can be used for CDC because the validity-period in ROW_START (Object starts to be valid) and ROW_END (Object is now invalid) can be interpreted when an INSERT-, UPDATE- or DELETE-query happened. But it's more cumbersome as with alternative CDC-variants.
INSERT:
Object was found for the first time
ROW_START is the insertion time
UPDATE:
Object wasn't found for the first time
ROW_START is the update time
DELETE:
ROW_END lies in the past
there is no new entry for this object in the next few lines
I'll add a picture to clarify this.
You can see that this versioning is space saving because you can combine the information about INSERT and DELETE of an object in one line, but to check for DELETEs is costly.
In the example above I used a Table with a clear Primary Key. So a check for the-same-object is easy: just look at the id. If you want to capture changes in talbes with an key-combination this can also make the whole process more annoying.
Edit: another point is that the protocol-Data is kept in the same table as the "real" data. Maybe this is faster for an INSERT than known alternativ solution like the tracking per TRIGGER (like here), but if changes are made quite frequent on the table and you want to process/analyse the CDC-Data this can cause performance problems.
MariaDB supports System-Versioned Tables since version 10.3.4. System version tables are specified in the SQL:2011 standard. They can be used for automatically capturing previous versions of rows. Those versions can then be queried to retrieve their values as they have been set at a specific point in time.
The following text and code example is from the official MariaDB documentation
With system-versioned tables, MariaDB Server tracks the points in time
when rows change. When you update a row on these tables, it creates a
new row to display as current without removing the old data. This
tracking remains transparent to the application. When querying a
system-versioned table, you can retrieve either the most current
values for every row or the historic values available at a given point
in time.
You may find this feature useful in efficiently tracking the time of
changes to continuously-monitored values that do not change
frequently, such as changes in temperature over the course of a year.
System versioning is often useful for auditing.
With adding SYSTEM VERSIONING to a newly created or an already existing table (using ALTER), the table will be expanded by row_start and row_end time stamp columns which allow retrieving the record valid within the time between the start and the end timestamps.
CREATE TABLE accounts (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(255),
amount INT
) WITH SYSTEM VERSIONING;
It is then possible to retrieve data as it was at a specific time (with SELECT * FROM accounts FOR SYSTEM_TIME AS OF '2019-06-18 11:00';), all versions within a specific time range
SELECT * FROM accounts
FOR SYSTEM_TIME
BETWEEN (NOW() - INTERVAL 1 YEAR)
AND NOW();
or all versions at once:
SELECT * FROM accounts
FOR SYSTEM_TIME ALL;
I have a table named Warehouse for my database, it has Warehouse_idWarehouse and Warehouse_name as primary keys. What i want to do is to efficiently store a maximum of N recent changes that have been made to each warehouse that is stored in the table. I have considered creating a "helper" table (e.g. warehouse_changes) and taking care of the updates through my application, but honestly it feels like there is a smarter way around this.
Is there a way to store a specific amount of entries per warehouse and automatically manage updating the right element through mysql workbench? Thanks in advance and keep in mind that i'm not particularly advanced in this field.
There is a very detailed article on O'Reilly Answers that describes how to do exactly what you want using triggers.
When explained in two words, you need to create a helper table and a trigger per each operation type that you want to store. For example, here's how a trigger for updates looks like according to that article:
-- Creating a trigger that will run after each update
-- for each affected row
CREATE TRIGGER au_warehouse AFTER UPDATE ON Warehouse FOR EACH ROW
BEGIN
-- Insert new values into a log table, or you can insert old values
-- using the OLD row reference
INSERT INTO warehouse_log (action, id, ts, name)
VALUES('update', NEW.id, NOW(), NEW.name);
END;
After that you can get the latest 1000 changes using a simple SQL query:
SELECT * FROM warehouse_log ORDER BY ts DESC LIMIT 1000;
I am working on some database project (PHP/MySQL) used for billing.
Whenever a new bill is created I want to generate a bill number consisting of year, week and increment number. I would like to do this with a trigger. The trigger will use the existing billnumbers to find the increment number or start with a fresh increment for the first bill n a new week and/or new year.
Apart from generating the bill number, I can do a BEFORE INSERT trigger and set the NEW.billnumber to the newly generated billnumber. It is also possible to do an AFTER INSERT and update the record with the generated billnumber.
My question is which one should I choose. BEFORE INSERT or AFTER INSERT? I did search for this, but I can't find a good argumentation when to use BEFORE or AFTER.
Found out that it can be done with BEFORE INSERT only because MySQL does not allow manipulation of the table that triggered the AFTER INSERT trigger.
I have a situation where I need to keep track of all changes to the data in a MySQL database.
For example, we have a field in the "customers" table which will contain a rating that indicates how risky it is to do business with that customer. Whenever this field is changed, I need to have it logged so we can go back and say "well they were a 3 and now they are an 8," for example. Is there any automated way to handle this in MySQL or am I just going have to write tons of change tracking logic into the application itself?
This is the type of thing that triggers are designed for inside of MySQL assuming you're using a 5+ version of MySQL.
CREATE TRIGGER log_change_on_table BEFORE UPDATE ON customers
FOR EACH ROW
BEGIN
INSERT INTO customer_log (customer_id, rating, date)
VALUES (OLD.customer_id, OLD.rating, now())
END $$
I want to remove a table row from my table new_data once the row is 45 mins old and then input it in another table called old_data.
The only way i can think for this to work, it to query the database lets say every min and remove any row thats (current_time - time inserted) > 45 mins.
Is there any other way of doing this? if not how could i set up a table to record inserted_time?
edit added
How could i write this statement to retrieve the correct data into the old_data table
SELECT * FROM new_spots WHERE (NOW()-created_at)>45mins
and then insert the above into the old_data table
you can specify value of time column upon insertion:
INSERT INTO x (created_at) VALUES (NOW());
additionally you can setup VIEW to show you only recent entries.
you are asking for some kind of auto expiration feature, it is not built into mysql. Memcached provides this feature. So it might be cleaner to achieve your goal as:
when you insert data into your system, you do:
insert your data into memcached with 45 minutes expiration time -- after 45 minutes, the data automatically disappear from memcached.
insert the data into the old_data table with a created_at column -- in case you need to rebuild your memcached when your memcached have to restart or other issue.
So everytime you just need to get the new data from the memcached -- as a side effect, it is faster than get the data from mysql :).
#keymone showed you how to capture the insert time. Then, periodically (every minute seems excessive - every 5 mins? 15 mins?) go through and build a list that meets the criteria, and for each entry, insert into your second table and delete from your first table.
I don't think there is an automatic way to do this. Here are some alternative ideas.
Use CRON
I have a similar scenario where we need to aggregate data from one table into another. A simple command line tool running via CRON suffices. We receive a few messages a second into our Web server and each results in a database insert. So volumes aren't huge but they are reasonably similar to your scenario
We use the NOW() function to record the insert time and after the records are 1hr old, we process them. It isn't exactly an hour but it is good enough. You can see the created_on field below.
CREATE TABLE glossaries (
id int(11) NOT NULL auto_increment,
# Our stuff ...
created_on datetime default NULL,
KEY owner_id (owner_id),
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Use CRON and a Trigger
Alternatively you could use a database trigger to kick off the processing. You would still need something scheduled to cause the trigger to fire but you would get max performance/
Chris