OK...not looking for code just yet. I'm making a change on how I handle a list of colleges.
I had one column in my a_players table called Offers. It was basically a CSV of Colleges that I exploded and sorted, but I would have to go in directly to the table to add to it. I want more flexibility and detail, including timestamp (Date), so I created a Colleges table and for each scholarship offer, an Offers table. All of this shows up on a Player's Profile.
Below is the query. The problem I'm having is how to handle the data from Offers table. I do have a FOREACH loop set up, which is how I handled the exploded and sorted from the CSV.
$query = "SELECT *,p.id as pid,p.city,p.school FROM a_players p
LEFT JOIN a_players_offers po
ON p.id = po.playerID
LEFT JOIN a_colleges c
ON po.collegeID = c.id
When I have a WHILE loop with the query results, if a kid has six offers, it prints all the profile information six times, including the College name. When I have an IF loop, it only prints the Player Profile once, but it also just prints the first college.
I think if I get some direction, I can produce the code myself. I just can't seem to find any samples when I have searched.
GROUP_CONCAT is the pathway for this, if anyone else comes across this with the same problem.
Related
I'm trying to loop all records displayed in a page, from the selected one to the end of the rows:
For example here, as I'm selecting only the 5th row it will loop through 5th and 6th row (as there are no more rows below)
What I've been trying is this:
ProdOrderLine := Rec;
REPEAT
UNTIL ProdOrderLine.NEXT = 0;
But it will loop through all records in the table which are not even displayed in the page...
How can I loop only the page records from the selected one to the latest?
Try Copy instead of assignment. Assignment only copies values of there field from one instance of record-variable to another, it died not copy filters or keys (sort order).
Alas, I have to mention that this is uncommon scenario to handle records like this in BC. General best practice approach would be to ask user to select all the records he or she needs with the shift+click, ctrl+click or by dragging the mouse. In that case you will use SetSelectionFiler to instantly grab ask the selected records.
This is how it works across the system and this how user should be taught to work. It is a bad idea to add a way to interact with record that only works in one page in the whole system even if users are asking for it bursting into tears. They probably just had this type of interaction in some other system they worked with before. I know this is a tough fight but it worth it. It is for the sake of stability (less coding = less bugs) and predictability (a certain way of interaction works across all the pages) of the system.
I have a table in a database which stores items. Each item has a unique ID, which the DB generates upon insertion (auto-increment).
A user may perform a specific task that will add X items to the database, however my program (C++ server application using MySQL connector) should return the IDs that the database generated right away. For example, if I add 6 items, the server must return 6 new unique IDs to the client.
What is the fastest/cleanest way to do such thing? So far I have been doing INSERT followed by SELECT for each new item OR INSERT followed by last_insert_id, however if there are 50 items to add it will take a few seconds at least which is not good at all for user experience.
sql_task.query("INSERT INTO `ItemDB` (`ItemName`, `Type`, `Time`) VALUES ('%s', '%d', '%d')", strName.c_str(), uiType, uiTime);
Getting the ID:
uint64_t item_id { sql_task.last_id() }; //This calls mysql_insert_id
I believe you need to rethink your design slightly. Let's use the analogy of a sales order. With a sales order (or invoice #) the user gets an invoice number (auto_incr) as well as multiple line item numbers (also auto_inc).
The sales order and all of the line items are selected for insert (from the GUI) and the inserts are performed. First, the sales order row is inserted and its id is saved in a variable for subsequent calls to insert the line items. But the line items are then just inserted without immediate return of their auto_inc id values. The application is merely returned the sales order number in the end. How your app uses that sales order number in subsequent calls is up to you. But it does not need to be immediate to retrieve all the X or 50 rows at once, as it has the sales order number iced and saved somewhere. Let's call that sales order number XYZ.
When you actually need the information, an example call could look like
select lineItemId
from lineItems
where salesOrderNumber=XYZ
order by lineItemId
You need to remember that in a multi-user system that there is no guarantee of receiving a contiguous block of numbers. Nor should it matter to you, as they are all attached appropriately with the correct sales order number.
Again, the above is just an analogy, used for illustration purposes.
That's a common but hard to solve problem. Unsure for mysql, but PostreSQL uses sequences to generate automatic ids. Inserting frameworks (object relationnal mappers) use that when they expect to insert many values: they query directly the sequence for a bunch of IDs and then insert new rows using those already known IDs. That way, no need for an additional query after each insert to get the ID.
The downside is that the relation ID - insertion time can be non monotonic when different writers intermix their inserts. It is not a problem for the database, but some (poorly written?) program could expect it is.
As you ID is autoincremental, you can do only two SELECT queries - before and after INSERT queries:
SELECT AUTO_INCREMENT FROM information_schema.tables WHERE table_name = 'dbTable' AND table_schema = DATABASE();
--
-- INSERT INTO dbTable... (one or many, does not matter);
--
SELECT LAST_INSERT_ID() AS lastID;
This will give you the siquence between first and last inserted IDs. Then you can easily calculate how many they are.
Alright I am in a rather difficult situation, or at least I think so anyway. I have been doing some research on how to fix my problem but have really come up empty handed.
I need to be able to reindex the rowid of my table after I delete a row. That way at any given time when I want to update or index a row by the rowid it is accessing the correct one.
Now for those of you asking why. Basically I am interfacing a "homebrewed" db that was programmed in C and is really just a bunch of memory locations all accessed like they were a db table. So what I'm trying to say is they can look up a row by searching for a value in the table, or by simply saying i want row 6. Lastly the table could consist of really anything, and any values which means they dont create a column as an index and ultimately the only thing for me to index their row by row number is the rowid to my knowledge.
So I have found that VACUUM would do what I want or need but it appears that the system that database is in isn't giving sqlite privileges to write so when VACUUM is run it comes back with and error. (ERROR 14 or Unable to open the database file) (I also know that my db is open so that isn't the issue but not having write privileges is the only reason I can come up with) I have also read some stuff about the auto increment or something like that but didn't really understand/think that was going to be able to fix my problem.
Any suggestions or ideas from the sqlite or database geniuses out that would be appreciated.
Not sure if I have understood completely your problem, but if you can use SQL code maybe you can write a query to update the IDs (assuming they are in dense order).
You can use a query like this:
UPDATE t1
SET id = (SELECT rank
FROM (SELECT id,
(
SELECT count()+1
FROM (SELECT DISTINCT id
FROM t1 AS t
WHERE t.id < t1.id
)
) rank
FROM t1
) AS sub
WHERE sub.id = t1.id
);
You can check my demo in SQLFiddler. In this demo you will see the result of the DELETE and UPDATE statements (to simulate your case) if you run all queries together.
I have been searching for a while on how to get the generated auto-increment ID from an "INSERT . INTO ... (...) VALUES (...)". Even on stackoverflow, I only find the answer of using a "SELECT LAST_INSERT_ID()" in a subsequent query. I find this solution unsatisfactory for a number of reasons:
1) This will effectively double the queries sent to the database, especially since it is mostly handling inserts.
2) What will happen if more than one thread access the database at the same time? What if more than one application accesses the database at the same time? It seems to me the values are bound to become erroneous.
It's hard for me to believe that the MySQL C++ Connector wouldn't offer the feature that the Java Connector as well as the PHP Connector offer.
An example taken from http://forums.mysql.com/read.php?167,294960,295250
sql::Statement* stmt = conn->createStatement();
sql::ResultSet* res = stmt->executeQuery("SELECT ##identity AS id");
res->next();
my_ulong retVal = res->getInt64("id");
In nutshell, if your ID column is not an auto_increment column then you can as well use
SELECT ##identity AS id
EDIT:
Not sure what do you mean by second query/round trip. First I thought you are trying to know a different way to get the ID of the last inserted row but it looks like you are more interested in knowing whether you can save the round trip or not?
If that's the case, then I am completely agree with #WhozCraig; you can punch in both your queries in a single statement like inser into tab value ....;select last_inserted_id() which will be a single call
OR
you can have stored procedure like below to do the same and save the round trip
create procedure myproc
as
begin
insert into mytab values ...;
select last_inserted_id();
end
Let me know if this is not what you are trying to achieve.
I am trying to lower the amount of queries that my django app is using, but I am a little confused on how to do it.
I would like to get a query set with one hit to the database and then filter items from that set. I have tried a couple of things, but I always get queries for each set.
let's say I want to get all names from my DB, but also separate out the people just named Ted. Both the names and the ted set will be used in the template.
This will give me two sets, one with all names and one with Ted.. but also hits the database twice:
namelist = People.objects.all()
tedList = namelist.filter(name='ted')
Is there a way to filter the first set without hitting the data base again?
tedList = [person for person in namelist if person.name == 'ted']
This will filter the initial QueryList on the client side.