I have a feed of data coming from KDB via TCP. It's working well, however I'm getting columns coming over the wire that I don't need. Is it possible to filter the columns on my subscription in the u.sub statement?
No, not out of the box. What you can do is update the upd function in r.q to select the columns that you actually want, which updates your local table in the realtime database.
You'd also need to initialise the table in r.q so that it doesn't get picked up automatically from the tickerplant on .u.sub
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I need to produce a trigger function that will fire, probably after update on one table that uses the data returned by that row insert to query data from a second table and return that data to the user.
Putting the function together should be OK I think, but, there is the possibility that the second table may not have the required data yet (I can't be sure the second table will be updated before this trigger fires).
Is there a way I can capture the fact that the return is null and put in a wait to try again a short time later?
Not getting any sense as to how I can do this from my searching.
OK, more contexts as requested. The tables are being loaded by an external process which reads csv files and imports the data into the database. The order of loading is not consistent so I can't (I don't think) rely on the second table being loaded when the trigger on the target tables fires.
In my model I want to loop through the database which contains multiple columns (see example) by an event. The idea behind it is that I want to create dynamic events based on the rows in the database.
But I've no clue how to iterate through a database in anylogic and also was not able to find an example of a loop with a database.
The dummycode of my problem would look something like this:
For order in orderdatabase:
Create order based on (order.name, order.quantity, order.arrivaltime, order.deliverylocation)
Where order in the loop is every row of the database, and the value on which the creation is based based on the different column values of that specific row.
Can somebody give me a simple example of how to create such a loop for this specific problem.
Thanks in advance.
Use the database query wizard:
put your cursor into a code field
this will allow you to open the database wizard
select what you need (in your case, you want the "iterate over returned rows and do something" option
Click ok
adjust the dummy code to make it do what you want
For details and examples, check the example models and the AnyLogic help, explaining all options in detail.
My flow is simple and I am just reading a raw file into a SQL table.
At times the raw file contains data corresponding to existing records. I do not want to insert a new record in that case and would only want to update the existing record in the SQL table. The challenge is, there is a 'record creation date' column which I initialize at the time of record creation. The update operation overwrites that column too. I just want to avoid overwriting that column, while updating the other columns from the information coming from the raw file.
So far I am having no idea about how to do that. Could someone make a recommendation?
I defaulted the creation column to auto-populate in the SQL database itself. And I changed my flow to just update the remaining records. Talend job is now not touching that column. Problem solved.
Yet another reminder of 'Simplification is underrated'. :)
I need to setup worldship to pull from one of our postgres databases. I need to have it so that the packages are sorted by id. I have no way (that i am aware of) of having worldship send the order by clause so I need to have the default for the records returned to be returned by id.
On a second note I have no idea how postgres default sorts it looks like it by the last time the record was changed so if i write a two records id 1,2 then change record 2 when I run the query it returns them with record 2 being first.
Rows are returned in an unspecified order, per sql specs, unless you add an order by clause. In Postgres, that means you'll get rows in, basically, the order that live rows read on the disk.
If you want a consistent order without needing to add an order by clause, create a view as suggested in Jack's comment.
There is no such thing as a "default sort". Rows in a table are not sorted.
You could fake this with a view (as suggested by Jack Maney) there is no way you can influence the order of the rows that are returned.
But if you do that, be aware that adding an additional ORDER BY to a SELECT based on that view will sort the data twice.
Another option might be to run the CLUSTER command on that table to physically order the rows on the disk according to the column you want. But this sill does not guarantee that the rows are returned in that order. Not even with a plain SELECT * FROM your_table (but chances are reasonably high for that).
You will need to re-run this statement on a regular basis because the order created by the CLUSTER command is not automatically maintained.
For what it's worth, which probably isn't much, from my testing, it appears that PostgreSQL's "default" ordering is based on the time the records were last updated. The most recently updated records will appear last. Note that I couldn't find any documentation to support this. It's just what I've found from my own testing.
You could eventually use a sorted index, which should guarantee you order of retrieved rows in case the query plan hits the index, or if you force it, but this approach will be more than circuitous :). ORDER BY clause is the way to go as mentioned already.
this is my first time using SQL at all, so this might sound basic. I'm making an iPhone app that creates and uses a sqlite3 database (I'm using the libsqlite3.dylib database as well as importing "sqlite3.h"). I've been able to correctly created the database and a table in it, but now I need to know the best way to get stuff back from it.
How would I go about retrieving all the information in the table? It's very important that I be able to access each row in the order that it is in the table. What I want to do (if this helps) is get all the info from the various fields in a single row, put all that into one object, and then store the object in an array, and then do the same for the next row, and the next, etc. At the end, I should have an array with the same number of elements as I have rows in my sql table. Thank you.
My SQL is rusty, but I think you can use SELECT * FROM myTable and then iterate through the results. You can also use a LIMIT/OFFSET(1) structure if you do not want to retrieve all elements at one from your table (for example due to memory concerns).
(1) Note that this can perform unexpectedly bad, depending on your use case. Look here for more info...
How would I go about retrieving all the information in the table? It's
very important that I be able to access each row in the order that it
is in the table.
That is not how SQL works. Rows are not kept in the table in a specific order as far as SQL is concerned. The order of rows returned by a query is determined by the ORDER BY clause in the query, e.g. ORDER BY DateCreated, or ORDER BY Price.
But SQLite has a rowid virtual column that can be used for this purpose. It reflects the sequence in which the rows were inserted. Except that it might change with a VACUUM. If you make it an INTEGER PRIMARY KEY it should stay constant.
order by rowid