I am trying to create a function that will accept name of tag and a datetime value and drop a extent within a specific table which has that tag and then ingest a new record into that table with the same tag and the input datetime value -- sort of 'update' simulation. I am not bothered about performance, it's just going to hold metadata -- maybe 20-30 rows at max.
So this is how the create table looks:-
.create table MyTable(sometext:string,somevalue:datetime)
And shown below is my function creation step, which is failing:-
.create-or-alter function MyFunction(arg_sometext:string,arg_somedate:datetime)
{
.drop extents <| .show table MyTable extents where tags has arg_sometext;
.ingest inline into table MyTable with (tags="[arg_sometext]") <| arg_somedate
}
So you can see I am trying to do something simple -- I am suspecting that Kusto won't allow commands in a function. Is there any workaround for achieving this?
Generally:
Kusto mandates that control commands start with a dot (.), and that this must be the first character in the text of the command. As queries, functions, etc. don't start with a dot, this precludes them from invoking control commands.
This is an intentional limitation that prevents a wide range of code injection attacks. By imposing this rule, Kusto makes it easy to guarantee that any query that does not begin with a dot will only have read access to the data and metadata, and never be able to alter them.
Specifically: with regards to your specific scenario:
I'm assuming it's triggered automatically (even if you did have the option to create a function), which suggests you should be able to achieve your goal using Kusto's API / Client libraries and a simple script/app.
An alternative, and perhaps even better approach, would be to re-consider if you actually need to delete or update specific records, or you can use summarize arg_max() in order to query for only the latest "versions" of the records (you could also create a function which encapsulates that logic and overrides the table, by naming the function with the table's name).
Related
I want to produce/update the output of a table using several functions. Becasue each functions will create separate columns. For me it would be relatively practical to write several functions for it.
To update a table using one function is documented in the documentation. https://learn.microsoft.com/en-us/azure/data-explorer/kusto/management/updatepolicy
https://learn.microsoft.com/en-us/azure/data-explorer/kusto/management/alter-table-update-policy-command
But this case is not informed. is it even possible to do it ? if so How ?
is is this right way to do this ? .set-or-append TABLE_NAME<| FUNCTION1 <| FUNCTION2 <| FUNCTION3
You can chain update policies as much as you need (as long as it does not create a circular reference), this means that Table B can have an update policy that runs a function over Table A and Table C can have an update policy that runs a function over Table B.
If you don't need the intermediate tables you can set their retention policy to 0 days, this means that no data will actually be ingested into these tables.
My R workflow now involves dealing with a lot of queries (RPostgreSQL library). I really want to make code easy to maintain and manage in the future.
I started loading large queries from separate .SQL files (this helped) and it worked great.
Then I started using interpolated values (that helped) which means that I can write
SELECT * FROM table WHERE value = ?my_value;
and (after loading it into R) interpolate it using sqlInterpolate(ANSI(), query, value = "stackoverflow").
What happens now is I want to use something like this
SELECT count(*) FROM ?my_table;
but how can I make it work? sqlInterpolate() only interpolates safely by default. Is there a workaround?
Thanks
In ?DBI::SQL, you can read:
By default, any user supplied input to a query should be escaped using
either dbQuoteIdentifier() or dbQuoteString() depending on whether it
refers to a table or variable name, or is a literal string.
Also, on this page:
You may also need dbQuoteIdentifier() if you are creating tables or
relying on user input to choose which column to filter on.
So you can use:
sqlInterpolate(ANSI(),
"SELECT count(*) FROM ?my_table",
my_table = dbQuoteIdentifier(ANSI(), "table_name"))
# <SQL> SELECT count(*) FROM "table_name"
sqlInterpolate() is for substituting values only, not other components like table names. You could use other templating frameworks such as brew or whisker.
I'd like to use flyway for a DB update with the situation that an DB already exists with productive data in it. The problem I'm looking at now (and I did not find a nice solution yet), is the following:
There is an existing DB table with numeric IDs, e.g.
create table objects ( obj_id number, ...)
There is a sequence "obj_seq" to allocate new obj_ids
During my DB migration I need to introduce a few new objects, hence I need new
object IDs. However I do not know at development time, what ID
numbers these will be
There is a DB trigger which later references these IDs. To improve performance I'd like to avoid determine the actual IDs every time the trigger runs but rather put the IDs directly into the trigger
Example (very simplified) of what I have in mind:
insert into objects (obj_id, ...) values (obj_seq.nextval, ...)
select obj_seq.currval from dual
-> store this in variable "newID"
create trigger on some_other_table
when new.id = newID
...
Now, is it possible to dynamically determine/use such variables? I have seen the flyway placeholders but my understanding is that I cannot set them dynamically as in the example above.
I could use a Java-based migration script and do whatever string magic I like - so, that would be a way of doing it, but maybe there is a more elegant way using SQL?
Many thx!!
tge
If the table you are updating contains only reference data, get rid of the sequence and assign the IDs manually.
If it contains a mix of reference and user data, you need to select the id based on values in other columns.
I need to be able to run a query such as
SELECT * FROM atable WHERE MyFunc(afield) = "some text"
I've written MyFunc in a VB module but the query results in "Undefined function 'MyFunc' in expression." when executed from .NET
From what I've read so far, functions in Access VB modules aren't available in .NET due to security concerns. There isn't much information on the subject but this avenue seems like a daed end.
The other possibility is through the CREATE PROCEDURE statement which also has precious little documentation: http://msdn.microsoft.com/en-us/library/bb177892%28v=office.12%29.aspx
The following code does work and creates a query in Access:
CREATE PROCEDURE test AS SELECT * FROM atable
However I need more than just a simple select statement - I need several lines of VB code.
While experimenting with the CREATE PROCEDURE statement, I executed the following code:
CREATE PROCEDURE test AS
Which produced the error "Invalid SQL statement; expected 'DELETE', 'INSERT', 'PROCEDURE', 'SELECT', or 'UPDATE'."
This seems to indicate that there's a SQL 'PROCEDURE' statement, so then I tried
CREATE PROCEDURE TEST AS PROCEDURE
Which resulted in "Syntax error in PROCEDURE clause."
I can't find any information on the SQL 'PROCEDURE' statement - maybe I'm just reading the error message incorrectly and there's no such beast. I've spent some time experimenting with the statement but I can't get any further.
In response to the suggestions to add a field to store the value, I'll expand on my requirements:
I have two scenarios where I need this functionality.
In the first scenario, I needed to enable the user to search on the soundex of a field and since there's no soundex SQL function in Access I added a field to store the soundex value for every field in every table where the user wants to be able to search for a record that "soundes like" an entered value. I update the soundex value whenever the parent field value changes. It's a fair bit of overhead but I considered it necessary in this instance.
For the second scenario, I want to normalize the spacing of a space-concatenation of field values and optionally strip out user-defined characters. I can come very close to acheiving the desired value with a combination of TRIM and REPLACE functions. The value would only differ if three or more spaces appeared between words in the value of one of the fields (an unlikely scenario). It's hard to justify the overhead of an extra field on every field in every table where this functionality is needed. Unless I get specific feedback from users about the issue of extra spaces, I'll stick with the TRIM & REPLACE value.
My application is database agnostic (or just not very religious... I support 7). I wrote a UDF for each of the other 6 databases that does the space normalization and character stripping much more efficiently than the built-in database functions. It really annoys me that I can write the UDF in Access as a VB macro and use that macro within Access but I can't use it from .NET.
I do need to be able to index on the value, so pulling the entire column(s) into .NET and then performing my calculation won't work.
I think you are running into the ceiling of what Access can do (and trying to go beyond). Access really doesn't have the power to do really complex TSQL statements like you are attempting. However, there are a couple ways to accomplish what you are looking for.
First, if the results of MyFunc don't change often, you could create a function in a module that loops through each record in atable and runs your MyFunc against it. You could either store that data in the table itself (in a new column) or you could build an in-memory dataset that you use for whatever purposes you want.
The second way of doing this is to do the manipulation in .NET since it seems you have the ability to do so. Do the SELECT statement and pull out the data you want from Access (without trying to run MyFunc against it). Then run whatever logic you want against the data and either use it from there or put it back into the Access database.
Why don't you want to create an additional field in your atable, which is atable.afieldX = MyFunc(atable.afield)? All what you need - to run UPDATE command once.
You should try to write a SQL Server function MyFunc. This way you will be able to run the same query in SQLserver and in Access.
A few usefull links for you so you can get started:
MSDN article about user defined functions: http://msdn.microsoft.com/en-us/magazine/cc164062.aspx
SQLServer user defined functions: http://www.sqlteam.com/article/intro-to-user-defined-functions-updated
SQLServer string functions: http://msdn.microsoft.com/en-us/library/ms181984.aspx
What version of JET (now called Ace) are you using?
I mean, it should come as no surprise that if you going to use some Access VBA code, then you need the VBA library and a copy of MS Access loaded and running.
However, in Access 2010, we now have table triggers and store procedures. These store procedures do NOT require VBA and in fact run at the engine level. I have a table trigger and soundex routine here that shows how this works:
http://www.kallal.ca/searchw/WebSoundex.htm
The above means if Access, or VB.net, or even FoxPro via odbc modifies a row, the table trigger code will fire and run and save the soundex value in a column for you. And this feature also works if you use the new web publishing feature in access 2010. So, while the above article is written from the point of view of using Access Web services (available in office 365 and SharePoint), the above soundex table trigger will also work in a stand a alone Access and JET (ACE) only application.
I need to apply two successive aggregate functions to a dataset (the sum of a series of averages), something that is easily and routinely done with common table expressions in SQL Server or another DBMS that supports CTEs. Unfortunately, I am currently stuck with SQLite which does not support CTEs. Is there an alternative or workaround for achieving the same result in SQLite without performing two queries and rolling up the results in code?
To add a few more details, I don't think it could be easily done with views because the first set of aggregate values need to be retrieved based on a WHERE clause with several parameters. E.g.,
SELECT avg(elapsedTime)
FROM statisticsTable
WHERE connectionId in ([lots of values]) AND
updateTime > [startTime] AND
updateTime < [endTime]
GROUP BY connectionId
And then I need the sum of those averages.
Now that we are in THE FUTURE, let me note here that SQLite now does support Common Table Expressions, as of version 3.8.3 of 2014-02-03.
http://www.sqlite.org/lang_with.html
Would this work?
SELECT SUM(t.time) as sum_of_series_of_averages
FROM
(
SELECT avg(elapsedTime) as time
FROM statisticsTable
WHERE connectionId in ([lots of values]) AND
updateTime > [startTime] AND
updateTime < [endTime]
GROUP BY connectionId
) as t
By converting your averages into an inline view, you can SUM() the averages.
Is this what you are looking for?
As you've mentioned, SQLite doesn't support CTEs, window functions, or any of the like.
You can, however, write your own user functions that you can call inside SQLite by registering them to the database with the SQLite API using sqlite_create_function(). You register them with the database, and then you can use them in your own application code. You can make an aggregate function that would perform the sum of a series of averages based on the individual column values. For each value, a step-type callback function is called that allows you to perform some calculation on the data, and a pointer for holding state data is also available.
In your SQL, then, you could register a custom function called sum_of_series_of_averages and have:
SELECT sum_of_series_of_averages(columnA,columnB)
FROM table
WHERE ...
For some good examples on how those work, you should check out the SQLite source code, and also check out this tutorial (search for Defining SQLite User Functions).