I would like to create a View that only returns new data added to the database since the last time the View was run. I know this sounds like a simple question, and there a millions of question just like it on here, but there are some restrictions in my case.
I can't use Stored Procedures, Functions or Triggers.
The user accessing the View only has read access to the database.
I posted a similar question here and was going to add an UPDATE statement to update a table with the current DateTime, and then check this table at the beginning of the View and only query after this DateTime. But the user accessing the View only has read access now.
I was also thinking there might be a type of timestamp column that updates to the current time when read with a SELECT statement, but apparently not.
Just for reference there is only ONE user accessing this view.
Any help much appreciated.
If the user only has read access to the database, then you have to store the relevant information at the application layer and not in the database. It simply is not possible to store information in the database if you don't have write access -- or at least information not part of some other process.
The recommendation would be for the application to keep track of the record returned -- keeping track of the maximum CreatedAt value or id. Then access the database using something like:
select v.*
from view v
where id > $id;
The subsequent code would update $id in the application.
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 have a column Quantity in a table Inventory of MySQL which gets updated from multiple sources. I needed to maintain a track in the table on another column called QuantityLog on the last updated time of the Quantity and the source which did it. Something like this should be the content of QuantityLog column (Text type) (only the latest update details is required):
<Log>
<UpdateTime>2015-02-23 12:00:01 PM</UpdateTime>
<Source> Feeder application</Source>
</Log>
I am aware of how to do it using trigger if only the update time is required. However, with the trigger approach is there any other mechanism to get the source and use this too?
Do note pls that I am trying to perform this via triggers only as any other mechanisms of using my application to do this will require me to change in all applications that make this change and I am not inclined to do that.
There is no way MySql can know the "feeder application", unless there is a variable or table filled with that value. If you have this, it is easy to create a trigger that updates this info into the Inventory table on each change of the Quantity field.
However, if your applications use unique mysql users to connect to the database, you can of course use the CURRENT_USER() built in function inside your TRIGGER. Alternatively, CONNECTION_ID() might be helpful when tracking who did what. For example, you can create a new table that logs the connection id of your application. In that table you could write the application name, the PID and other stuff. Of course this would mean to change our application a bit by adding the appropriate insert statement after a connection is established. The overhead should be small, since usually connections are held in pools and do not get re-created all the time.
I have a database in MySQL. The values in column named Curr_BaL is updated by different operations performing on it. The application, which is written in Java, accesses that database. When it runs, by default it should retrieve the last updated value. However, I also want to be able to get the value at a specific DATE entered by the user.
I have tried to do my best, but have not successful yet, and my whole application depends on that data.
Your problem is not entirely clear. What I can understand is that you need a way to have your users aware of this "last updated" value.
You have several designs approach for this. I think that the simpler would be to fetch this value when you're authenticating your user, and set it to its session information, so it will be available at any time.
You can also have some kind of service caching this value (since I guess is the same for all users).
A very important thing you didn't mentioned is who updates this value, is an external application? is a process on the same application?.
What I can understand, users date more priority then automaticaly date. Simple way for it's using triggers. Below may be useful:
CREATE OR ALTER trigger on_table_ins for TABLE
active before insert position 0
AS
BEGIN
IF (NEW.DATEFIELD IS NULL) THEN NEW.DATEFIELDD='now';
END
It correct for firebird, so see manual for triggers and insert current date(time) for your RDBMS.
In MySQL I have a single database with one schema. In Microsoft Sql Server it is recommended to use a "Tenant View Filter" so in Microsoft Sql Server this gives me exactly what I need.
CREATE VIEW TenantEmployees AS
SELECT * FROM Employees WHERE TenantID = SUSER_SID()
What is the best way to accomplish the same in MySQL? An equivalent to the "Tenant View Filter" will work if it is performs well.
Thanks!!
The query you suggest (that I could find in MSDN) has text afterwards that explains exactly what are its assumptions. In particular, it mentions that it assumes that the "owner" of a row in the Employees table is specified in the TenantID field that is populated according to the SID of the user(s) you are partitioning for.
What that means is that you can replicate the same idea whatever way you decide to implement your data as long as you have clearly defined partitions of the data and know exactly how to associate it with the table you are creating a view for.
In particular, if you configure your system so that each partition accesses the DB with its own credentials, you could use the CURRENT_USER or USER constructs of MySQL as the IDs defining your partitions and the query to create the view would be basically the same as the one suggested in MSDN replacing SUSER_ID with CURRENT_USER.
But if you use the same user to access from all the partitions, then the suggested method is irrelevant on either database server.
Since you need to use your tenantId value to perform filtering, a table valued user defined function would be ideal, as a view normally does not accept parameters. Unfortunately, unlike many other database products MySQL doesn't support table-valued functions. However, there are MySQL hacks that claim to emulate parametrized views. These could be useful for you.
It's a little tricky in MySQL, but it can be done:
CREATE OR REPLACE VIEW {viewName}
AS
SELECT {fieldListWithoutTenantID}
FROM {tableName}
WHERE (id_tenant = SUBSTRING_INDEX(USER( ),'#',1))
I wrote up a full blog post on how I converted a single-tenant MySQL application to multi-tenant in one weekend with minimal changes. https://opensource.io/it/mysql-multi-tenant/
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.