I have basic knowledge of MS SQL which actually sabotages me as the syntax differs from MySQL in which I need the code written.
I have X databases named "project_%". It's 1 database per project. I need a script or a procedure (it's gonna be rarely used by support) that's gonna take some user info from master DB and add a list of users (or at least a single user) into all (later a list might be required) "project_%" databases.
My idea was to create a variable/temp table to fill with the list of databases and run a cycle (for/while) to set a default schema and insert required data. This is where I'm stuck as I have no idea how to set default schema from a variable or to input the variable into variable_db.table.
What I've found so far always differed from what I needed and couldn't apply it to my code.
Thanks,
Z
Related
So I'm kind of stumped.
I have a MySql project that involves a database table that is being manipulated and altered by scripts on a regular basis. This isn't so unusual, but I need to automate a script to run (after hours, when changes aren't happening) that would save the result of the following:
SHOW CREATE TABLE [table-name];
This command generates the ready-to-run script that would create the (empty) table in it's current state.
In SqlWorkbench and Navicat it displays the result of this SHOW command in a field in a result set, as if it was the result of a SELECT statement.
Ideally, I want to take into a variable in a procedure, and change the table name; adding a '-mm-dd-yyyy' to end of it, so I could show the day-to-day changes in the table schema on an active server.
However, I can't seem to be able to do that. Unlike a Select result set, I can't use it like that. I can't get it in a variable, or save it to a temporary, or physical table or anything. I even tried to return this as a value in a function, from which I got the error that a function cannot return a result set - which explains why it's displayed like one in the db clients.
I suspect that this is a security thing in MySql? If so, I can totally understand why and see the dangers exposed to a hacker, but this isn't a public-facing box at all, and I have full root/admin access to it. Hopefully somebody has already tackled this problem before.
This is on MySql 8, btw.
[Edit] After my first initial comments, I need to add; I'm not concerned about the data with this question whatsoever, but rather just these schema changes.
What I'd really -like- to do is this:
SELECT `Create Table` FROM ( SHOW CREATE TABLE carts )
But this seems to be mixing apples and oranges, as SHOW and SELECT aren't created equal, although they both seem to return the same sort of object
You cannot do it in the MySQL stored procedure language.
https://dev.mysql.com/doc/refman/8.0/en/show.html says:
Many MySQL APIs (such as PHP) enable you to treat the result returned from a SHOW statement as you would a result set from a SELECT; see Chapter 29, Connectors and APIs, or your API documentation for more information. In addition, you can work in SQL with results from queries on tables in the INFORMATION_SCHEMA database, which you cannot easily do with results from SHOW statements. See Chapter 26, INFORMATION_SCHEMA Tables.
What is absent from this paragraph is any mention of treating the results of SHOW commands like the results of SELECT queries in other contexts. There is no support for setting a variable to the result of a SHOW command, or using INTO, or running SHOW in a subquery.
So you can capture the result returned by a SHOW command in a client programming language (Java, Python, PHP, etc.), and I suggest you do this.
In theory, all the information used by SHOW CREATE TABLE is accessible in the INFORMATION_SCHEMA tables (mostly TABLES and COLUMNS), but formatting a complete CREATE TABLE statement is a non-trivial exercise, and I wouldn't attempt it. For one thing, there are new features in every release of MySQL, e.g. new data types and table options, etc. So even if you could come up with the right query to produce this output, in a couple of years it would be out of date and it would be a thankless code maintenance chore to update it.
The closest solution I can think of, in pure MySQL, is to regularly clone the table structure (no data), like so:
CREATE TABLE backup_20220618 LIKE my_table;
As far as I know, to get your hands on the full explicit CREATE TABLE statement, as a string, would require the use of an external tool like mysqldump which was designed specifically for that purpose.
I updated the SCHEMA of a live table in MySQL for use in my multi-user database. Each user has their own db and links to the production tables through ODBC.
I have been receiving a write error while trying to test my schema updates. I cannot find the core reason. I hypothesized that because the other users are in the production table but have not been relinked to update the table SCHEMA; That it is causing a conflicting write error on my relinked table.
I added a TINYINT with No NULLS and default value of 0
I double checked all datatypes for incompatibility & have tested the "non relinked" tables in a older version of the DB and confirmed it is working as intended with no errors
I expect/want to be able to edit records without a write error, but am hesitant to update the other users to the new table if it is currently having write errors
After changing the schema of a linked table, it's required to refresh the link on all Access databases connected to it.
You can do this on the ribbon through external data -> linked table manager.
Unfortunately, either all users that have a database need to do this manually, unless you automate the task on startup through vba.
You have two separate issues. To "see" new columns, then yes, you must re-link the tables.
(so above is separate question and separate issue). You thus as a general rule can add new columns to the database (even while in use). However, the client side linked tables will not see the new columns until such time you re-link. This approach (adding new columns, but not yet re-linked from Access) is certainly ok and fine - the only downside is end users can't see nor use the new columns until such time you link. From a developer point of view, this good - since your users will not see nor find new columns until such time you roll out a new front end to each work station.
Ok, now problem and issue number two.
As for adding a new column, then re-linking, and THEN having some issue is really a separate issue. In most cases, if you attempting to use a tiny int as a Boolean (and I think that is your case), then you need to ensure several things:
Do not allow nulls (you seem to have this ok).
Make sure you set a default of 0 (server side) for this column. (you might have not allowed nulls, but without a default, then Access likely will still complain. And this default is important during creating time - since the new column needs to be "filled" with zeros.
Make sure the table has a PK defined.
Consider adding a row version column (I think mySQL has these, not sure but they can help immensely).
I needed to insert some initial (default) data into a new database and I found this Inserts tab on MySQL Workbench EER Diagram table editing form
My assumption was that I can use it to insert initial (default) data that will get propagated to the database during synchronization (not sure how it will get merged with any existing data in the database though...). I added couple rows and synced model with an empty database, but no data was inserted.
So, my question is what this Inserts tab is for on the Table Editing screen?
I use MySQL Workbench 6.
P.S. If somebody can also point to an easy way to insert initial (default) data (except simply running a SQL script) I will appreciate it.
Thank you.
The data added on the INSERTs page is indeed thought to be like an initial set of (test)data. It doesn't consider existing data however. I think it is also only used if you do forward engineering, not on synchronization.
Other ways of inserting data always involve an SQL script, that's what the (text) API is about for SQL servers. But you can add scripts to your model too (see the overview page). They are not run automatically, however.
After reading a few articles here and around, I have realised that database version control in a development team is actually of high importance.
Until now I have been using a simple dump whole database each time there is an update, if only 1 table was altered sometimes we can get away with just dumping the single table then reimporting. Not the best but it works quite well, for additive changes and we haven't had any hiccups yet.
Now, I save a .mwb (Mysql Workbench diagram) file in the git repository of the project I'm working on.
Then I also use dbv for schema management, along with git, with each branch being named based on the project and it's working quite well. This allows me to version schematic changes with the ability to revert or rollback.
However, what about the data contained in the tables. How can this be maintained? Maybe I'm better off just sticking with the old method. I understand on projects with the same DB structure but different data that's fine but what about sites with specific database data that needs to be versioned and managed.
Also what about the base of already deployed sites that need database changes, how can this be seamless. Some have suggested the use of update/alter scripts and that works fine with default values and such. But what if I have made a change on a website platform that requires every websites database to be changed, and keep the data intact?
I've worked mostly in business application development and configuration management. Your question is representative for the challenges in such an environment; when you upgrade for instance Microsoft Word, you don't need to change all documents right away from doc to docx. And the documents even have a more simple structure a full relation database.
Not so for business applications; users skip releases, make unauthorized changes to the data model and the system needs to keep running and providing the correct numbers...
We use for our own applications (largest one is like 600 tables) a self-developed CASE tool which includes branching/merging, but the approach can also be done manually.
Versioning Datamodel
The data model can be written down in a structured way. For instance as table contents (CSV to be loaded in a table with meta data) or as code that detects the version in use and adds columns and tables when missing, including non-trivial migrations.
This even allows multiple users at the same time to change the data model.
When you use auto-detection (for instance, we use a call named "verify_column" instead of "add_column"), this even allows smooth migration independent of the release number the customer is starting the upgrade from. Such a procedure analyzes the table to be changed and issues the correct DDL such as alter table t1 add col1 number not null when a column is missing or alter table t1 modify col1 not null when the column was already present but nullable.
For Oracle and SQL Server I can provide you with a few sample procedures. In MySQL I would code this using a client side language, preferably OS independent to allow installations to run on Windows and Linux. Maybe using Apache Ant when you have experience with that.
Versioning Data
We split the tables in four categories:
R: referential data; data the application site must provide before he actually use the system. For instance, general ledger account codes. The referential data seldomly changes after go live and does not continuously grow in size. The contents reflect the site's business model where the application is used.
T: transaction data; data the site registers, changes and removes during use of the application. For instance, general ledger entries. The transaction data starts at 0 an grows continuously. When company doubles in revenues, transaction data also doubles.
S: seeded data; data NOT maintained by the user at the site but provided and maintained by the developing party. Essentially this is code turned into data. For example, 'F' stands for 'Female'. Errors in seeded data can lead to system errors.
O: the rest (ideally not needed, since they are technical, but some systems require a temporary table A or a scratch table B).
The contents of tables of category 'S' (seeded data) is placed under version control. We normally register these as metadata in our case tool, then named 'data sets', but you can also use for instance Microsoft Excel or even code.
For example, in Excel you would have a list of rows of seeded data. In column A you might enter an Excel function like =B..&"|"&C..& "|" & ... which concatenates everything and makes it suitable for loading by a loader tool.
For example in code, you might have a call like:
verifySeed('TABLE_A', 'CODE', 'VALUE')
The Excel is a little bit hard to bring under version control allowing multiple users to change contents at the same time. The approach with code is very simple.
Please remember to also add features to remove obsoleted seeded data. For instance, by explicitly listing obsoleted seeded data or by automatically removing all seeded data present in the tables but not touched by the last installation.
You would need to keep a journal of transactions on your datamodel that is synchronised to your code versions. For each update that adds information (i.e. a new field) you can simply enter the statements like 'ALTER TABLE x ADD COLUMN y ...' and provide a DEFAULT VALUE (with a function perhaps) in an update script. And a 'ALTER TABLE x REMOVE COLUMN y ...' for the downdate script. You would need to export your data before you truncate information in a table. You can convert the dumped table data to SQL for the inverse transaction so that you can add the missing information using these.
You can use a 'journal' table within your data-model to keep track of these transactions using simple ordinals that denote the applied scripts. Whenever the software is installed it can compare these numbers to create a list of transactions to play to move the database from state N to state X, backwards or forwards, without losing any data!
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.