I have a persisted computed column in one table with the value calculated using a user function. How can I force that column to be updated without updating any other column in that table?
UPDATE: So as it turns out, this will not work as I imagined it.
I wanted to have user function that contains sub-query in it, gets me some data and stores it in computed column. But SQL Server won't allow this...
It looks like I will have to do something similar with insert/update triggers.
If you persist the value by adding the PERSISTED keyword, the value is both retained on insert and will be synchronized when the referenced column is updated.
Related
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'. :)
When I try to update a database with some modified values in a dataset, a concurrence exception doesn't raise if i change manually some values in the database after the fill method on the dataset is performed. (I only get the exception if I delete a row manually and then I try call the method update of data adapter).
How should I check if I have a "dirty read" on my dataset?.
You have several options.
Keeping a copy of the original entity set to compare against and make
the is dirty determination at the point you need to know whether it's
dirty.
Checking the datarow's rowstate property and if Modified compare
the values in the Current and Original DataRowVersions. If the second
change makes the value the same as the original then you could call
RejectChanges, however that would reject all changes on the row. You
will have to manually track each field since the dataset only keeps
per-row or per-table changes.
how would I ignore having Zend_DB save() from trying to fill out a created column? I do not need that column for a certain model.
Don't send the data. save() is part of the Zend_Db_Table_Row api and is designed to be somewhat intelligent in the way it saves data to a row. It will perform an insert or an update of a row depending on what is required.
save() will also only update the columns that it has data for. If you don't send new data for your created column save() won't overwrite the data.
When ever it is possible I let the database I'm using create and update the columns for created and updated. That way I have the information available to query if I need it but I don't have to do something with PHP that My database can do better.
Check out http://framework.zend.com/manual/1.12/en/zend.db.table.html Section "Advanced usage".
For more specific and optimized requests, you may wish to limit the
number of columns returned in a row or rowset. This can be achieved by
passing a FROM clause to the select object. The first argument in the
FROM clause is identical to that of a Zend_Db_Select object with the
addition of being able to pass an instance of Zend_Db_Table_Abstract
and have it automatically determine the table name.
Important
The rowset contains rows that are still 'valid' - they simply contain
a subset of the columns of a table. If a save() method is called on a
partial row then only the fields available will be modified.
So, if you called an update() I think it would be as simple as unsetting the value for the column you don't want to touch. Of course database constraints will need to be honored - i.e. column should allow nulls.
I want to dynamically access SQLite result set. Since webworks/javascript doesnt support "PRAGMA table_info(table_name); I am saving all newly created tables information in a single two column table called schema. schema has two columns, table_name and column_name.
So I created a function to access table data dynamically. I use the item=results.rows.item(i) and than access row data with item.column.
column is a variable that is assigned the value from schema, representing the column_name. When I alert(column) I get the correct column_name, but when I used item.column my results are "undefined".
any advice on how to resolve this matter.
If I understand you correctly, column is a variable that holds the value of a column name, and you want to access that column from the results item. If that's the case, then this might help:
//Assuming "var column" has already been defined,
//and given the value of the column name to be accessed in the results item.//
var item = results.rows.item(i);
var columnValue = item[column];
I struggled with this too, and this is what I found/use. You put in brackets the variable containing the column name, and that's how you access it.
EDIT: This is obviously Javascript stuff, and what I used for accessing SQLite in PhoneGap. Hopefully it helps.
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