a) SqlCommand.ExecuteNonQuery is used for update, insert and delete operations.
Besides the fact that by using ExecuteNonQuery instead of ExecuteReader we automatically know there won’t be any query results returned, are there some other benefits/reasons why ExecuteNonQuery should be used?
b) Similarly, if we want a database operation to return a single value, we should use ExecuteScalar instead of ExecuteNonquery ,where with the latter result would be returned via SqlParameter. Is there any particular reason why we should prefer ExecuteScalar over ExecuteNonQuery?
thanx
For the 2nd point...
ExecuteScalar returns 1st column of 1st row: the entire dataset is passed back to the client. Even if the dataset is exactly one row and exactly one column, it's still less efficient to return a dataset than use an output/return parameter
The same applies to the 1st point too: more efficient to not process a recordset.
For the 1st point...
You have said:
we automatically know there won’t be any query results returned
Actually, ExecuteNonQuery returns the number of affected rows, which is very important if your logic after executing the query depends on whether the database has been changed or not.
Related
Using RODBCext (and Teradata) my SQL query often need to be restricted and is done so with a where statement. However, this is not always required and it would be beneficial to not restrict, but I would like to use a single SQL query. (The actual query is more complex and has several instances of what I'm attempting to apply here)
In order to return all rows, using a wildcard seems like the next best option, but nothing appears to work correctly. For example, the sql query is:
SELECT *
FROM MY_DB.MY_TABLE
WHERE PROC_TYPE = ?
The following does work when passing in a string for proc_type:
sqlExecute(connHandle, getSQL(SQL_script_path), proc_type, fetch = TRUE)
In order to essentially bypass this filter, I would like to pass a wildcard so all records are returned.
I've tried proc_type set to '%', '*'. Also escaped both with backslashes and enclosed with double-quotes, but no rows are ever returned, nor are any errors produced.
You could use COALESCE to do this:
SELECT *
FROM MY_DB.MY_TABLE
WHERE PROC_TYPE = COALESCE(?, PROC_TYPE);
In the event that your parameter is NULL it will choose PROC_TYPE to compare to PROC_TYPE which will return everything.
As for your wildcard attempt you would have to switch over to an operator that can use a wildcard. Instead of =, LIKE for instance. I think you would end up with some oddball edge cases though depending on your searchterm and the data in that column, so the COALESCE() option is a better way to go.
Using Python 3 and sqlite, I perform a query that gives me results I want to iterate over. But, as part of what I want to do in the iteration, I want to perform a second query. But, when I do the second query, the results from the first query are destroyed by the second query and my script stops iterating over the first query because there is nothing left from the first query to iterate over (hoping this makes sense!). Is it possible to have 2 or more query results in the same script unaffected by each other? Or, what is a good/best way to resolve this issue?
Here's an example of what I mean:
curs.execute('SELECT number1, number2, FROM numbers WHERE ID = 3')
for row in curs:
do this (whatever?)
do this (whatever?)
curs.execute('UPDATE table1 SET ID = "foo" WHERE state = "bar"')
conn.commit()
Not an expert but they should have unique names.
I have following declaration for collection
TYPE T_TABLE1 IS TABLE OF TABLE_1%ROWTYPE INDEX BY BINARY_INTEGER;
tbl1_u T_TABLE1;
tbl1_i T_TABLE1;
This table will keep growing and at the end, will be used in FORALL loop to do insert or update on TABLE_1.
Now there might be cases, where I want to delete a certain element. So i am planning to create a procedure, which will take the KEY (unique) and matched the element if that key is found
PSEDUO CODE
FOR i in tbl1_u.FIST..tbl1_u.LAST
LOOP
if tbl1_u(i).key = key then
tbl1.delete(i);
end if;
END LOOP;
My question is,
Once i delete the particular element, would be collection adjust automatically i.e., the index i would be replaced by next element or would that particular index will remain null/invalid and could possibly give me exception if i use it in FORALL INSERT/UPDATE?
I don't think that i can pass TABLE_1%ROWTYPE object to a procedure, do i have to create a record type ?
Any other tip regarding managing collection for bull delete/update/insert would be appreciate. Remeber, I would be dealing with 2 tables, if i am inserting/updating in table_1 then it means i am deleting it from table_2 and vice-versa.
Given that TABLE_1.KEY is unique you might consider using that as the index to your associative arrays. That way you can delete from the collections using the KEY value, which according to the pseudocode is available when doing the deletions. This would also save you having to iterate through the table to find the KEY you want, as the KEY would be the index - so your "deletion" pseudo-code would become:
tbl1_u.delete(key);
To answer your questions:
Since you're using associative arrays, when an element is deleted there is no "empty" space in the collection. The indexes for the elements, however, don't actually change. Therefore you need to use the collection.PRIOR and collection.NEXT methods to loop through the collection. But again, if you use the KEY value as the index you may not need to loop through the collections at all.
You can pass a TABLE_1%ROWTYPE as a parameter to a PL/SQL procedure or function.
You might want to consider using a MERGE statement which could handle doing the inserts and updates in one step. This might allow you to maintain only a single collection. Might be worth looking in to.
Share and enjoy.
I want to restrict the execution of my PL/SQL code from repetition. That is, I have written a PL/SQL code with three input parameters viz, Month, Year and a Flag. I have executed the procedure with the following values for the parameters:
Month: March
Year : 2011
Flag: Y
Now, If I am trying to execute the procedure with the same values to the parameters as above, I want to write some code in the PL/SQL to restrict the unwanted second execution. Can anyone help. I hope the question is no ambiguous.
You can use the function result cache: http://www.oracle-developer.net/display.php?id=504 . So Oracle can do this for you.
I would create another table that would store the 3 parameters of each request. When your procedure is called it would first check the "parameter request" table to see if the calling parameters have beem used before. If found, then exit the procedure. If not found, then save the parameters and execute the rest of the procedure.
Your going to need to keep "State" of the last call somewhere. I would recommend creating a table with a datetime column.
When your procedure is called update this table. So, next time when your procedure is called.. check this table to see when was the last time your procedure was called and then proceed accordingly.
Why not set up a table to track what arguments you've already executed it with?
In your procedure, first check that table to see if similar parameters have already been processed. If so, exit (with or without an error).
If not, insert them and do the processing necessary.
Depending on how tight the requirements are, you'll need to get a exclusive lock on that table to prevent concurrent execution.
A nice plus would be an extra column with "in progress"/"done"/"error" status so that you can check if things are going on properly. (Maybe a timestamp too if that's important/interesting.)
This setup allows you to easily clear some of the executions (by deleting some rows) if you find things need to be re-done for whatever reason.
Make an insert in the beginning of the procedure, and do a select for update tolock the table so no one else can process any data and if everything goes ok with the procedure, commit and release the table 😀
Im trying to change the information on each row depending on the result from the query. Im thinking that at the minute my problem is that I'm only returning the first result from the query into the result.
e.g. query returns row 1 with '1232' row 2 '1243' but result is only ever set to '1232'
I could be wrong but its why I'm here :)
You say that your SQL returns multiple rows, but are using the ExecuteScalar() to run it. ExecuteScalar will only return a single result, ie the first column of the first row. Sounds like you need to fill a datatable using a SQLDataAdapter or something else to do what you're looking for.
Also it would be beneficial if you included your SQL statement as rlb indicated.