I have a MS Access database with a table of data from the university accounting system and another table with data from our local invoice system. I want to find the invoices in the local table that are not in the university accounting system table. The invoice number (as text, because our invoice numbers may have text) is my match point between the two tables.
The problem is that some of the unmatched invoice numbers SHOULD have found a match. The numbers appear to be exactly the same in both tables. When I query either table for a specific unmatched invoice number, I find it. The formatting of both table’s invoice number field is the same. An example is invoice number 100512. The same number is in both tables but my query says no match found.
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Given two DynamoDB tables: Books and Words, how can I create an index that associates the two? Specifically, I'd like to query to get all Books that contain a certain Word, and query to get all Words that appear in a specific Book.
The objective is to avoid scanning an entire table for these queries.
Based on your question I can't tell if you only care about unique words or if you want every word including duplicates. I'll assume unique words.
This can be done with a single table and a Global Secondary Index.
Create a table called BookWords with a Hash key of bookId and a Sort key of word. If you Query this table with a bookId you will get all of the unique words in that book.
Create a Global Secondary Index with a Hash key of word and a Sort key of bookId. If you Query this index with a word you will get all of the bookIds of books that contain that word.
Depending of your use case, you will probably want to normalize the words. For example, is "Word" the same as "word"?
If you want all words, not just unique words, you can use a similar approach with a few small changes. Let me know
I have a sqlite table containing metadata extracted from thousands of audio files in a directory tree. The objective of the extraction is to run a series of queries against the table to identify and rectify anomalies in the underlying metadata. The corrected metadata is then written back from the table to the underlying files. The underlying files are grouped into albums with each album in a directory of its own. Table structure relevant to my question is as follows:
__path: unique identifier being the path and source filename combined
__dirpath: in simple terms represents the directory from which the file represented by a table record was drawn. Records making up an album will have the same __dirpath
__discnumber: number designating the disc number from which the track originates. The field can be blank or contain a string 1,2,3... etc.
I'd like to identify all records where (__dirpath is identical and __discnumber equals 1).
SELECT DISTINCT __dirpath,
discnumber
FROM alib
WHERE __dirpath IN (
SELECT __dirpath
FROM alib
GROUP BY __dirpath
HAVING count( * ) > 0
)
AND
discnumber = 1
ORDER BY __dirpath,
discnumber;
I want to make unique constraint in cassandra .
As i want to all the value in my column be unique in my column family
ex:
name-rahul
phone-123
address-abc
now i want that i this row no values equal to rahul ,123 and abc get inserted again on seraching on datastax i found that i can achieve it by doing query on partition key as IF NOT EXIST ,but not getting the solution for getting all the 3 values uniques
means if
name- jacob
phone-123
address-qwe
this should also be not inserted into my database as my phone column has the same value as i have shown with name-rahul.
The short answer is that constraints of any type are not supported in Cassandra. They are simply too expensive as they must involve multiple nodes, thus defeating the purpose of having eventual consistency in first place. If you needed to make a single column unique, then there could be a solution, but not for more unique columns. For the same reason - there is no isolation, no consistency (C and I from the ACID). If you really need to use Cassandra with this type of enforcement, then you will need to create some kind of synchronization application layer which will intercept all requests to the database and make sure that the values are unique, and all constraints are enforced. But this won't have anything to do with Cassandra.
I know this is an old question and the existing answer is correct (you can't do constraints in C*), but you can solve the problem using batched creates. Create one or more additional tables, each with the constrained column as the primary key and then batch the creates, which is an atomic operation. If any of those column values already exist the entire batch will fail. For example if the table is named Foo, also create Foo_by_Name (primary key Name), Foo_by_Phone (primary key Phone), and Foo_by_Address (primary key Address) tables. Then when you want to add a row, create a batch with all 4 tables. You can either duplicate all of the columns in each table (handy if you want to fetch by Name, Phone, or Address), or you can have a single column of just the Name, Phone, or Address.
suppose we have a file with just one table named TableA and this table has just one column named Text;
let say we populate our TableA with 3,000,000 of strings like these(each line a record):
Many of our patients are incontinent.
Many of our patients are severely disturbed.
Many of our patients need help with dressing.
if I save the file at this level it'll be: ~326 MB
now let say we want to increase the speed of our queries and therefore we set our Text column as the PrimaryKey(or create index on it);
if I save the file at this level it'll be: ~700 MB
our query:
SELECT Text FROM "TableA" where Text like '% home %'
for the table without index: ~5.545s
for the indexed table: ~2.231s
As far as I know when we create index on a column or set a column to be our PrimaryKey then sqlite engine doesn't need to refer to table itself(if no other column was requested in query) and it uses the index for query and hence the speed of query execution increases;
My question is in the scenario above which we have just one column and set that column to be the PrimaryKey too, then why sqlite holds some kind of unnecessary data?(at least it seems unnecessary!)(in this case ~326 MB) why not just keeping the index\PrimaryKey data?
In SQLite, table rows are stored in the order of the internal rowid column.
Therefore, indexes must be stored separately.
In SQLite 3.8.2 or later, you can create a WITHOUT ROWID table which is stored in order of its primary key values.
I'm new to DynamoDB - I already have an application where the data gets inserted, but I'm getting stuck on extracting the data.
Requirement:
There must be a unique table per customer
Insert documents into the table (each doc has a unique ID and a timestamp)
Get X number of documents based on timestamp (ordered ascending)
Delete individual documents based on unique ID
So far I have created a table with composite key (S:id, N:timestamp). However when I come to query it, I realise that since my id is unique, because I can't do a wildcard search on ID I won't be able to extract a range of items...
So, how should I design my table to satisfy this scenario?
Edit: Here's what I'm thinking:
Primary index will be composite: (s:customer_id, n:timestamp) where customer ID will be the same within a table. This will enable me to extact data based on time range.
Secondary index will be hash (s: unique_doc_id) whereby I will be able to delete items using this index.
Does this sound like the correct solution? Thank you in advance.
You can satisfy the requirements like this:
Your primary key will be h:customer_id and r:unique_id. This makes sure all the elements in the table have different keys.
You will also have an attribute for timestamp and will have a Local Secondary Index on it.
You will use the LSI to do requirement 3 and batchWrite API call to do batch delete for requirement 4.
This solution doesn't require (1) - all the customers can stay in the same table (Heads up - There is a limit-before-contact-us of 256 tables per account)