I have this situation. Starting from a table, I have to check all the records that match a key. If records are found, I have to check another table using a key from the first table and so on, more on less on five levels. There is a way to do this in a recursive way, or I have to write all the code "by hand"? The language I am using is Visual Fox Pro. If this is is not possible, is it al least possible to use recursion to popolate a treeview?
You can set a relation between tables. For example:
USE table_1.dbf IN 0 SHARED
USE table_2.dbf IN 0 SHARED
SET ORDER TO TAG key_field OF table_2.cdx IN table_2
SET RELATION TO key_field INTO table_2 ADDITIVE IN table_1
First two commands open table_1 and table_2. Then you have to set the order/index of table_2. If you don't have an index for the key field then this will not work. The final command sets the relation between the two tables on the key field.
From here you can browse both tables and table_2's records will be filtered based on table_1's key field. Hope this helps.
If the tables have similar structure or you only need to look at a few fields, you could write a recursive routine that receives the name of the table, the key to check, and perhaps the fields you need to check as parameters. The tricky part, I guess, is knowing what to pass down to the next call.
I don't think I can offer any more advice without at least seeing some table structures.
Sorry for answering so late, but the problem was of course that the recursion wasn't a viable solution since I had to search inside multiple tables. So I resolved by doing a simple 2-Level search in the tables that I needed.
Thank you very much for the help, and sorry again for answering so late.
Related
I have designed my database in such a way that One of my table contains 52 columns. All the attributes are tightly associated with the primary key attribute, So there is no scope of further Normalization.
Please let me know if same kind of situation arises and you don't want to keep so many columns in a single table, what is the other option to do that.
It is not odd in any way to have 50 columns. ERP systems often have 100+ columns in some tables.
One thing you could look into is to ensure most columns got valid default values (null, today etc). That will simplify inserts.
Also ensure your code always specifies the columns (i.e no "select *"). Any kind of future optimization will include indexes with a subset of the columns.
One approach we used once, is that you split your table into two tables. Both of these tables get the primary key of the original table. In the first table, you put your most frequently used columns and in the second table you put the lesser used columns. Generally the first one should be smaller. You now can speed up things in the first table with various indices. In our design, we even had the first table running on memory engine (RAM), since we only had reading queries. If you need to get the combination of columns from table1 and table2 you need to join both tables with the primary key.
A table with fifty-two columns is not necessarily wrong. As others have pointed out many databases have such beasts. However I would not consider ERP systems as exemplars of good data design: in my experience they tend to be rather the opposite.
Anyway, moving on!
You say this:
"All the attributes are tightly associated with the primary key
attribute"
Which means that your table is in third normal form (or perhaps BCNF). That being the case it's not true that no further normalisation is possible. Perhaps you can go to fifth normal form?
Fifth normal form is about removing join dependencies. All your columns are dependent on the primary key but there may also be dependencies between columns: e.g, there are multiple values of COL42 associated with each value of COL23. Join dependencies means that when we add a new value of COL23 we end up inserting several records, one for each value of COL42. The Wikipedia article on 5NF has a good worked example.
I admit not many people go as far as 5NF. And it might well be that even with fifty-two columns you table is already in 5NF. But it's worth checking. Because if you can break out one or two subsidiary tables you'll have improved your data model and made your main table easier to work with.
Another option is the "item-result pair" (IRP) design over the "multi-column table" MCT design, especially if you'll be adding more columns from time to time.
MCT_TABLE
---------
KEY_col(s)
Col1
Col2
Col3
...
IRP_TABLE
---------
KEY_col(s)
ITEM
VALUE
select * from IRP_TABLE;
KEY_COL ITEM VALUE
------- ---- -----
1 NAME Joe
1 AGE 44
1 WGT 202
...
IRP is a bit harder to use, but much more flexible.
I've built very large systems using the IRP design and it can perform well even for massive data. In fact it kind of behaves like a column organized DB as you only pull in the rows you need (i.e. less I/O) rather that an entire wide row when you only need a few columns (i.e. more I/O).
I have an assignment where I have two tables. Both of these two tables have multiple records that can be grouped by a certain ID creating record sets within those two tables
Those record sets can have various number of records. The trick is I have to compare those two tables and compare them by those record sets. If one record set ordered by update date (one of the record fields) doesn't find an identical record set in another table, I have to output that record set
What is the best way to do it? How do I compare two different tables by record groups/record sets/record blocks?
Should I use sub-query factoring? Should I temporary tables? Should I use something else?
Thank you very much for your generous responses and please let me know if I made my question unclear
i guess you just need a minus query to show the differences.
If you use Toad there is a specific function. Or you can use the minus operator or read this other post link
Say i have something like this:
somerecord SOMETABLE%ROWTYPE;
Is it possible to access the fields of somerecord with out knowing the fields names?
Something like somerecord[i] such that the order of fields would be the same as the column order in the table?
I have seen a few examples using dynamic sql but i was wondering if there is a cleaner way of doing this.
What i am trying to do is generate/get the DML (insert query) for a specific row in my table but i havent been able to find anything on this.
If there is another way of doing this i'd be happy to use but would also be very curious in knowing how to do the former part of this question - it's more versatile.
Thanks
This doesn't exactly answer the question you asked, but might get you the result you want...
You can query the USER_TAB_COLUMNS view (or the other similar *_TAB_COLUMN views) to get information like the column name (COLUMN_NAME), position (COLUMN_ID), and data type (DATA_TYPE) on the columns in a table (or a view) that you might use to generate DML.
You would still need to use dynamic SQL to execute the generated DML (or at least generate static SQL separately).
However, this approach won't work for identifying the columns in an arbitrary query (unless you create a view of it). If you need that, you might need to resort to DBMS_SQL (or other tools).
Hope this helps.
As far as I know there is no clean way of referencing record fields by their index.
However, if you have a lot of different kinds of updates of the same table each with its own column set to update, you might want to avoid dynamic sql and look in the direction of statically populating your record with values, and then issuing update someTable set row = someTableRecord where someTable.id = someTableRecord.id;.
This approach has it's own drawbacks, like, issuing an update to every, even unchanged column, and thus creating additional redo log data, but I believe it should be considered.
I am writing a simple program to insert rows into a table.But when i started writing the program i got a doubt. In my program i will get duplicate input some times. That time i have to notify the user that this already exists.
Which of the Following Approaches is good to Use to achieve this
Directly Perform Insert statement will get the primary key violation error if it is duplicate notify otherwise it will be inserted. One Query to Perform
First make a search for the primary key values. If found a Value Prompt User. Otherwise perform insert operation.For a non-duplicate row this approach takes 2 queries.
Please let me know trade-offs between these approaches. Which one is best to follow ?
Regards,
Sunny.
I would choose the 2nd approach.
The first one would cause an exception to be thrown which is known to be very expensive...
The 2nd approach would use a SELECT count(*) FROM mytable WHERE key = userinput which will be very fast and the INSERT statement for which you can use the same DB connection object (assuming OO ;) ).
Using prepared statements will pre-optimize the queries and I think that will make the 2nd approach much better and mre flexible than the first one.
EDIT: depending on your DBMS you can also use a if not exists clause
EDIT2: I think Java would throw a SQLExcpetion no matter what went wrong, i.e. using the 1st approach you wouldn't be able to differ between a duplicate entry or an unavailable database without having to parse the error message - which is again a point for using SELECT+INSERT (or if not exists)
Anyone ever see how fogbugz sorts their tables? When you click to sort the column, they actually break the table up into many small tables that have each category of info.
Wondering if anyone knows how they do this?
Looking to implement this feature.
If you take a look through the cases page, and sort you can see what I mean.
Any help would be AWESOME!
Still Haven't figured this one out.
EDIT: #Peter, I don't want to postback and recreate a table every time the header title is clicked for a sort. I also want to know if their is a generic solution for this. If I click on the header to sort, by the way of javascript, it seperates the "one" table into many and I want to know if their is any generic solution for this because its just a MUCH better way of viewing a sorted Table.
EDIT: I do need a javascript sorter, but if you look right down at the implementation of fogbugz, it produces a different result...
Yup, Rich got it (I coded this feature into FogBugz a long while back).
If you have to do this on the client you have no choice but to sort the data, iterate through it generating table row after table row, and every time you hit a new sort value you create a new thead w/ the appropriate information.
To be honest it would be a pretty cool modification to this jQuery plugin: http://tablesorter.com/docs/ and you'd be able to leverage a lot of their work. If you're going to put in the time and create a general solution, might as well make it accessible to the community.
Without knowing specifically how Fog Creek accomplishes this, the way that I would do it is to output a table header, then iterate through the list, outputting a footer and a new header each time the group value changed.
Not sure what answer do you expect. SQL query for this would simply use ordering on selected column, and UI would start new table each time this value changes.
Here is screenshot of FogBugz with this sorting, after clicking on Priority column.
http://img297.imageshack.us/img297/6974/76755363ee3.png
Of course, starting new table doesn't make sense for every column (title, case #).
Edit: If I understand correctly, you're looking for a way how to do this in a browser without loading new page. If this is the case, I would suggest at least some server-side support, which would return your data in correct order, and properly structured for subtables (in xml/json/whatever you use). Your javascript will use this data to recreate tables. I am sure others with more web-ui experience will provide you with better answers.
I've used the Sortable Tables script from Kryogenix with some good results.
I don't know if it is relevant, but we store the results of a query in a temporary table in SQL, and then reference current-row-less-one to see if a Category has changed, and indicate this in the resulset.
In some instances we "indicate" this with a column containing
<tr><td colspan=999>Category Heading</td></tr>
so that the web page can just "inject" that into the table it is building.
SELECT Col1, Col2, ...,
[CATEGORY] = CASE WHEN T1.CategoryCol <> COALESCE(T2.CategoryCol, '')
THEN '<tr><td colspan=999>' + T1.CategoryCol + '</td></tr>'
ELSE ''
END
FROM #MyTempTable AS T1
LEFT OUTER JOIN #MyTempTable AS T2
ON T2.ID = T1.ID - 1