I'm trying to use a simple mysql database but tweak it so that every field is backed up up to an indefinite number of versions. The best way I can illustrate this is by replacing each and every field of every table with a stack of all the values this field has ever had (each of these values should be timestamped). I guess it's kind of like having customized version control for all my data..
Any ideas on how to do this?
The usual method for "tracking any changes" to a table is to add insert/update/delete trigger procedures on the table and have those records saved in a history table.
For example, if your main data table is "ItemInfo" then you would also have an ItemInfo_History table that got a copy of the new record every time anything changed (via the triggers).
This keeps the performance of your primary table consistent, yet gives you access to the history of any changes if you need it.
Here are some examples, they are for SQL Server but they demonstrate the logic:
My Repository table
My Repository History table
My Repository Insert trigger procedure
My Repository Update trigger procedure
Hmm, what you're talking about sounds similar to Slowly Changing Dimension.
Be aware that version control on arbitrary database structures is officially a rather Hard Problem. :-)
A simple solution would be to add a version/revision field to the tables, and whenever a record is updated, instead of updating it in place, insert a copy with the changes applied and the version number incremented. Then when selecting, always choose the record with the latest version. That's roughly how most such schemes are implemented (e.g. Wikimedia does it pretty much this exact way).
Maybe a tool can help you to do that for you. Have a look at nextep designer :
https://github.com/christophefondacci/nextep-designer
With this IDE you will be able to take snapshots of your database structure and data and put it under version control. After this you can compute the differences between any 2 versions and generate the appropriate SQL that can insert / update / delete your data.
Maybe this is an alternative way to achieve what you wanted.
Related
I have a schema of a database and a web application. I want to have the web application be able to select, insert and remove rows to a table, but the table may not exist, maybe in a testing environment, and the table may be missing columns, most likely because the web application has updated.
I want to be able to make sure that the table is ready to accept the data that the web application sends to it during the time the application is alive.
The idea I had is the application (written in Java) will have a table structure embedded into it, and when the application starts, just copy all of the data in the table (if it exists) to a temporary table, delete the old table and make a new one with the temporary table's data, and then drop the temporary table. As you can tell, it's nowhere near innovative.
Another idea I had is use the SHOW COLUMNS command to correct any missing columns parallel with the SHOW TABLES LIKE to check if it exists, but I feel like Stack Overflow would've had a better solution. Is that all I can do?
There are many ways to solve the problem of consistency of the database version and the version of the application.
However, in the production database, this situation is unacceptable.
I think that the simplest ways are the best.
To ensure such compliance, it is enough to execute a script that updates the database before performing the testing.
START TRANSACTION;
DROP TABLE ... IF EXISTS;
CREATE TABLE ...
COMMIT;
Remember about IF EXISTS and having DROP grant!
Such a script can be easily managed by placing it in RCS and controlling the version number needed in the application.
You can also save this version number in some table in the database itself and check when the application starts, whether the number is compatible with the assumed one and if you do not call the database update script.
Have a look at JPA an Hibernate. There is hbm2ddl.auto property. Looks like "update" option does what you want.
For more details
What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do
Sorry if this is a simple question but i have a problem.
I have been adding new columns to many tables in my local db . i.e MYSQL
I want to deploy the changes to production database and i have not maintained any text file to mention the changes i have made.
So how to get created or updated datetime of columns added to existing tables?
The table which might contain this information would be the INFORMATION_SCHEMA.COLUMNS table. The only problem is that it doesn't appear to record a timestamp when a column was added/altered. I can offer a workaround which might be just as fast. You may run SHOW CREATE TABLE on the table running in production, and then do the same on your dev version. Then, just use any reputable diff checking tool (e.g. DiffChecker.com) and look for the differences.
Moving forward, you should keep better track of the changes you make to your table during development. A much better approach, I think, would be to just keep track of the alter statements which you run on the table. Then, deploy these changes when you send everything to production.
I am very new to this and a good friend is in a bind. I am at my wits end. I have used gui's like navicat and sqlyog to do this but, only manually.
His band info data (schedules and whatnot) is in a MYSQL database on a server (admin server).
I am putting together a basic site for him written in Perl that grabs data from a database that resides on my server (public server) and displays schedule info, previous gig newsletters and some fan interaction.
He uses an administrative interface, which he likes and desires to keep, to manage the data on the admin server.
The admin server db has a bunch of tables and even table data the public db does not need.
So, I created tables on the public side that only contain relevant data.
I basically used a gui to export the data, then insert to the public side whenever he made updates to the admin db (copy and paste).
(FYI I am using DBI module to access the data in/via my public db perl script.)
I could access the admin server directly to grab only the data I need but, the whole purpose of this is to "mirror" the data not access the admin server on every query. Also, some tables are THOUSANDS of rows and parsing every row in a loop seemed too "bulky" to me. There is however a "time" column which could be utilized to compare to.
I cannot "sync" due to the fact that the structures are different, I only need the relevant table data from only three tables.
SO...... I desire to automate!
I read "copy" was a fast way but, my findings in how to implement were too advanced for my level.
I do not have the luxury of placing a script on the admin server to notify when there was an update.
1- I would like to set up a script to check a table to see if a row was updated or added on the admin servers db.
I would then desire to update or insert the new or changed data to the public servers db.
This "check" could be set up in a cron job I guess or triggered when a specific page loads on the public side. (the same sub routine called by the cron I would assume).
This data does not need to be "real time" but, if he updates something it would be nice to have it appear as quickly as possible.
I have done much reading, module research and experimenting but, here I am again at stackoverflow where I always get great advice and examples.
Much of the terminology is still quite over my head so verbose examples with explanations really help me learn quicker.
Thanks in advance.
The two terms you are looking for are either "replication" or "ETL".
First, replication approach.
Let's assume your admin server has tables T1, T2, T3 and your public server has tables TP1, TP2.
So, what you want to do (since you have different table structres as you said) is:
Take the tables from public server, and create exact copies of those tables on the admin server (TP1 and TP2).
Create a trigger on the admin server's original tables to populate the data from T1/T2/T3 into admin server's copy of TP1/TP2.
You will also need to do initial data population from T1/T2/T3 into admin server's copy of TP1/TP2. Duh.
Set up the "replication" from admin server's TP1/TP2 to public server's TP1/TP2
A different approach is to write a program (such programs are called ETL - Extract-Transform-Load) which will extract the data from T1/T2/T3 on admin server (the "E" part of "ETL"), massage the data into format suitable for loading into TP1/TP2 tables (the "T" part of "ETL"), transfer (via ftp/scp/whatnot) those files to public server, and the second half of the program (the "L") part will load the files into the tables TP1/TP2 on public server. Both halfs of the program would be launched by cron or your scheduler of choice.
There's an article with a very good example of how to start building Perl/MySQL ETL: http://oreilly.com/pub/a/databases/2007/04/12/building-a-data-warehouse-with-mysql-and-perl.html?page=2
If you prefer not to build your own, here's a list of open source ETL systems, never used any of them so no opinions on their usability/quality: http://www.manageability.org/blog/stuff/open-source-etl
I think you've misunderstood ETL as a problem domain, which is complicated, versus ETL as a one-off solution, which is often not much harder than writing a report. Unless I've totally misunderstood your problem, you don't need a general ETL solution, you need a one-off solution that works on a handful of tables and a few thousand rows. ETL and Schema mapping sound scarier than they are for a single job. (The generalization, scaling, change-management, and OLTP-to-OLAP support of ETL are where it gets especially difficult.) If you can use Perl to write a report out of a SQL database, you probably know enough to handle the ETL involved here.
1- I would like to set up a script to check a table to see if a row was updated or added on the admin servers db. I would then desire to update or insert the new or changed data to the public servers db.
If every table you need to pull from has an update timestamp column, then your cron job includes some SELECT statements with WHERE clauses based on the last time the cron job ran to get only the updates. Tables without an update timestamp will probably need a full dump.
I'd use a one-to-one table mapping unless normalization was required... just simpler to my opinion. Why complicate it with "big" schema changes if you don't have to?
some tables are THOUSANDS of rows and parsing every row in a loop seemed too "bulky" to me.
Limit your queries to only the columns you need (and if there are no BLOBs or exceptionally big columns in what you need) a few thousand rows should not be a problem via DBI with a FETCHALL method. Loop all you want locally, just make as few trips to the remote database as possible.
If a row is has a newer date, update it. I will also have to check for new rows for insertion.
Each table needs one SELECT ... WHERE updated_timestamp_columnname > last_cron_run_timestamp. That result set will contain all rows with newer timestamps, which contains newly inserted rows (if the timestamp column behaves like I'd expect). For updating your local database, check out MySQL's ON DUPLICATE KEY UPDATE syntax... this will let you do it in one step.
... how to implement were too advanced for my level ...
Yes, I have actually done this already but, I have to manually update...
Some questions to help us understand your level... Are you hitting the database from the mysql client command-line or from a GUI? Have you gotten to the point where you've wrapped your SQL queries in Perl and DBI, yet?
If the two databases have different, you'll need an ETL solution to map from one schema to another.
If the schemas are the same, all you have to do is replicate the data from one to the other.
Why not just create identical structure on the 'slave' server to the master server. Then create a small table that keeps track of the last timestamp or id for the updated tables.
Then select from the master all rows changed since the last timestamp or greater than the id. Insert them into the matching table on the slave server.
You will need to be careful of updated rows. If a row on the master is updated but the timestamp doesn't change then how will you tell which rows to fetch? If that's not an issue the process is quite simple.
If it is an issue then you need to be more sophisticated, but without knowing the data structure and update mechanism its a goose chase to give pointers on it.
The script could be called by cron every so often to update the changes.
if the database structures must be different on the two servers then a simple translation step may need to be added, but most of the time that can be done within the sql select statement and maybe a join or two.
Is there any way to automatically create a trigger on creation of new table in MySQL?
As I've pointed out in your other question, I think a process and security review is in order here. It's an audited database, so nobody (especially third-party service providers) should be creating tables in your database without your knowledge.
The issue you've got is, as well as the new table being created, you will also need to have another table created to store the audited/changed records, which will have an identical structure as the original table with possibly a time/date and user column. If a third-party provider is creating this table, they won't know to create the auditing table, therefore even if you could generate your triggers dynamically, they wouldn't work.
It's impossible to create a single table that will hold all changes record for all other tables in your database because the structure between tables inevitably differs.
Therefore: make all change requests (e.g. providers wants to create TableX, they submit a change request (including the SQL script) explaining the reason for the change) to yourself and/or your team.
You execute the SQL on a test copy of your database, and use the same structure to create another table to hold the modified records.
You then create and test the necessary triggers, generate a new SQL script to create the two tables and your triggers and execute that on your live database. You give your provider permissions to use the new table and away they go.
Everyone's happy. Yes, it may take a little while longer, and yes you'll have more work to do, but that's a hell of a lot less work than is required to try and parse query logs to re-create records that have already been changed/deleted, or parse the binary log and keep up-to-date with every change, and modify your code when the format of the log file changes etc etc.
I need to convert data that already exists in a MySQL database, to a SQL Server database.
The caveat here is that the old database was poorly designed, but the new one is in a proper 3N form. Does any one have any tips on how to go about doing this? I have SSMS 2005.
Can I use this to connect to the MySQL DB and create a DTS? Or do I need to use SSIS?
Do I need to script out the MySQL DB and alter every statement to "insert" into the SQL Server DB?
Has anyone gone through this before? Please HELP!!!
See this link. The idea is to add your MySQL database as a linked server in SQL Server via the MySQL ODBC driver. Then you can perform any operations you like on the MySQL database via SSMS, including copying data into SQL Server.
Congrats on moving up in the RDBMS world!
SSIS is designed to do this kind of thing. The first step is to map out manually where each piece of data will go in the new structure. So your old table had four fields, in your new structure fileds1 and 2 go to table a and field three and four go to table b, but you also need to have the autogenerated id from table a. Make notes as to where data types have changed and you may need to make adjustments or where you have required fileds where the data was not required before etc.
What I usually do is create staging tables. Put the data in the denormalized form in one staging table and then move to normalized staging tables and do the clean up there and add the new ids as soon as you have them to the staging tables. One thing you will need to do if you are moving from a denormalized database to a normalized one is that you will need to eliminate the duplicates from the parent tables before inserting them into the actual production tables. You may also need to do dataclean up as there may be required fileds in the new structure that were not required in the old or data converstion issues becasue of moving to better datatypes (for instance if you stored dates in the old database in varchar fields but properly move to datetime in the new db, you may have some records which don't have valid dates.
ANother issue you need to think about is how you will convert from the old record ids to the new ones.
This is not a an easy task, but it is doable if you take your time and work methodically. Now is not the time to try shortcuts.
What you need is an ETL (extract, transform, load) tool.
http://en.wikipedia.org/wiki/Extract,_transform,_load#Tools
I don't really know how far an 'ETL' tool will get you depending on the original and new database designs. In my career I've had to do more than a few data migrations and we usually always had to design a special utility which would update a fresh database with records from the old database, and yes we coded it complete with all the update/insert statements that would transform data.
I don't know how many tables your database has, but if they are not too many then you could consider going the grunt root. That's one technique that's guaranteed to work after all.
If you go to your database in SSMS and right-click, under tasks should be an option for "Import Data". You can try to use that. It's basically just a wizard that creates an SSIS package for you, which it can then either run for you automatically or which you can save and then alter as needed.
The big issue is how you need to transform the data. This goes into a lot of specifics which you don't include (and which are probably too numerous for you to include here anyway).
I'm certain that SSIS can handle whatever transformations you need to do to change it from the old format to the new. An alternative though would be to just import the tables into MS SQL as-is into staging tables, then use SQL code to transform the data into the 3NF tables. It's all a matter of what your most comfortable with. If you go the second route, then the import process that I mentioned above in SSMS could be used. It will even create the destination tables for you. Just be sure that you give them unique names, maybe prefixing them with "STG_" or something.
Davud mentioned linked servers. That's definitely another way that you can go (and got my upvote). Personally, I prefer to copy the tables over into MS SQL first since linked servers can sometimes have weirdness, especially when it comes to data types not mapping between different providers. Having the tables all in MS SQL will also probably be a bit faster and saves time if you have to rerun or correct portions of the data. As I said though, the linked server method would probably be fine too.
I have done this going the other direction and SSIS works fine, although I might have needed to use a script task to deal with slight data type weirdness. SSIS does ETL.