I'm tasked to work on a web based SQL simulator much like what can be found on SQL Fiddle or the one on W3Schools' SQL Tryit editor. Here are the requirements for the simulator:
Multiple Students will be using the simulator at the same time.
The teacher should be able to see or track their changes and queries.
DDL should be included (e.g, CREATE, ALTER, DROP DATABASES & TABLES), of course certain privileges are enforced as to not ruin the database.
And also a simulation using MySQL directly obviously won't work. So, to anyone who has a suggestion on how to go about doing this, that would be awesome.
Hmmm quite a difficult task you got there...
I would try an approach like this:
Create a sample database with some entries and tables based on the task for the students
Whenever a students logs in and starts the task, copy this sample database for this specific user
Create an input field for all MySQL commands in your view and an execute button
Whenever the student clicks on execute: log his input and maybe the current database state to a log and execute the command on the database created for the user and return the return values you get from MySQL (errors, messages or selects) to the user
This approach is easy and reliable because the student can't harm another database besides his own (provided the database rights are configured correctly) and he can just restore the database from the sample database if he f*cked up.
It should also meet your requirements:
Multiple students can work on it simultaneously: Check
The teacher can track their changes: Check
DDL is possible and the student can't harm anything besides his own DB: Check
Related
I am doing research on MySQL data. I used the dbConnect function to connect to the database and used dbReadTable to read a table.
My question is: if I start cleaning data to make it tidy using tidyr and dplyr, etc, will this change the data from the database (data that is stored in mySQL and was collected by researcher)
Or does cleaning data in R only change the data called upon in R and have NO EFFECT ON THE database.
I need a definitive, well-backed, and professional answer as the data I'm dealing with is pretty important and valuable.
Given a database connection, you can definitely modify data in the database by using any of the keywords such as INSERT, UPDATE, DELETE depending on the role of the database user;
One safe way to avoid any modification of the database is ask the database administrator (I assume you are not the one) to create a user that has only read access to it, and then connect the database using this specific user. Then you would be safe to do analysis without unintentionally injecting anything into your database because the database won't allow you to do so;
But most importantly consult with the database administrator before taking next step, this answer is just for giving a clue on how to do this safely from my personal perspective. No responsibility taken for the next move you made.
guys!
I need to ask you a question... I'm mew in programming business and if this question seems silly, please indulge me.
I have a little site where people have to register in order to post something. So I register every user in the database. I log into the db with:
$pdo = new PDO("mysql:host=localhost;dbname="MY-DB", "My-USER", "My-password");
The question is: when I log into the databse to do whatever operation I need (select, update, delete, insert) how many users ("MY-USER") should I create to login to the db ? Should I create one db-user for every users that registers on my site, or one one single user is enough to do the operations ?
Thanks.
In normal situations you should have additionally to a root user, which can create new databases and add new users, you should create one user per application which is accessing the database, so that a bug in one application wouldn't affect another.
In your case this means to have 1 additional user for your web application which has all permissions on one mysql-database and can create the necessary tables as well as read / modify data in those.
You should not use mysql as your user manager, instead create a table with the users, their (hashed) passwords, ... and manage them in your application.
I have a web application which takes sql queries and produces the output in the form of a report. I don't want the user to MODIFY the existing database any way. To do this I decided to block all the CREATE,ALTER,DELETE,DROP commands at the web application level by just looking at the first word of the supplied query. This would stop the user from altering the existing schema or the instance of the database.
Recently I discovered that Microsoft SQL Server has the command SELECT * INTO NEW_TABLE FROM OLD_TABLE which allows us to create a copy of the the existing table. Are there any more commands of this kind which would allow us to modify the schema or instance of the existing DB by passing the web application filter ?
Any better ways to block the commands according to my requirements are also welcomed but I do not wish to take away the freedom of creating report using SQL queries at the cost of security.
Why Cannot I use Grant
I see that grant is one good option that I see from the comment as well as the answers but I will not be able to use them because the user supplies the DB details which I use to create the report along with the username and password. It is for the DB's table the user points to that I create the report
You can generate the reports from results of a query performed by a user with only read permissions. This implies management of the database connection to allow other parts of the application to manipulates the data ( you will need to connect as different users).
CREATE USER 'foouser'#'localhost' IDENTIFIED BY 'barpass';
GRANT SELECT ON db.table TO 'foouser'#'localhost';
Even if you use "SELECT * INTO NEW_TABLE FROM OLD_TABLE" you have to create the new_table first using create statement then you can use that statement.
I am looking for a solution to the following:
Database: A
Table: InvoiceLines
Database: B
Table: MyLog
Every time lines are added to InvoiceLines in database A, I want to run a query that updates the table MyLog in database B. And I want it instantly.
Normally I would create a trigger in database A on INSERT in InvoiceLines. The problem is that database A belongs to a ERP program where I don't want to make any changes at all (updates, unknown functionality in 3-layer program, etc)
Any hints to help me in the right direction...?
You can use transactional replication to send changes from your table in database A to a copy in DB B, then create your triggers on the copy. It's not "instant," but it's usually considered "near real time."
You might be able to use DB mirroring to do this somehow, but you'd have to do some testing to see if you could get it to work right (maybe set up triggers in the mirror that don't exist in the original?)
One possible solution to replicate trigger's functionality without database update is to poll the table by an external application (i.e. java) which on finding new insert would fire required query.
In SQLServer2008, something similar can be done via C# assembly but again this needs to be installed which requires database update.
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.