Im still new with DynamoDB , How do I query something based on the previous query result?
This is how my table look like :
I want to query for the list of project info for an user.
From my first query , the result of USER#001 have [PROJECT#001,PROJECT#002].
Then I want to get a list project detail based on the first query.
How do I make an "nested" query ?? or is there anyway there I can query more efficiently ?
*The table structure is fix, I cant change it.
You can't. That's not the way DDB works...
All you could do is a BatchGetItem() with the pk & sk for the two projects.
Or if you don't happen to know the SK, you'd need to make two individual Query() calls with the pk only.
Related
I'm using the current version of PeopleSoft and I'm using their Query manager. I've built a query that looks at the job table and a customized version of the job table (so I can see future hires). In order to do this I've created a union. Everything works fine, except now I want to do a count of the job codes.
When I put in a count, I get an error. I don't know how to get it to work properly. I also don't really know how to using the 'having' tab.
I've attached some screenshots, including the SQL code.
SQL:
Having tab
You have a criteria in your query:
AND COUNT(*) = A.JOBCODE
Your job codes are string values that uniquely identify a job. It will never be equal to a count.
If you remove that criteria, your query will work:
The bigger issue is, what do you want to count? If your query was simply:
SELECT DEPTID, JOBCODE, COUNT(*)
This will give the count of employees in this department and job code. In your description, you said that you wanted the count of job codes. But each row has JOBCODE on it. The count of job codes on the row is one. What do you really want? The count of job codes in the database? The count of job codes in the result set?
If you want to get anything other than the count of rows within the group, you are not able to put that logic in PeopleSoft Query. You will need to create a view in AppDesigner and then you can add that to the query.
I have games table.
To keep it simple, I will add only two fields for the question.
gameId:
deadlineToPlay:
I want to query for all games with deadlineToPlay > than today.
How would I set up the index for this? I thought I could create an index with just deadlineToPlay, but if I understand correctly when querying on hashkey, it has to be exact value. Can't use >.
I would also not like to use a scan, due to costs.
A way to workaround this would be to create or use an existing field which will have constant value (for example, field hasDeadline with value true).
Now you can create the table key like this: hasDeadline as HASH key and deadlineToPlay as SORT key (if the table is already created, you can define this key in a new GSI).
This way you will be able to query by hasDeadline = true and deadlineToPlay > today.
I have a simple table consisting of orderID as PK and userID as SK, I found out that in dynamoDB you need to specify both PK and SK to use query. so in this case, how is it possible for me to get all the orders for userID x since I can't ignore orderID since they're the partition key of this table? another way to solve this which works but not recomended is using a scan filter, which scans the whole table then filters the result. it will eventually slow down as the table grow. I wonder how do you guys do it with this scenario?
You can create a Global Secondary Index (GSI) based on userId and query based on that index.
You can read more about indexes and GSI’s in the AWS docs here.
I enjoy working with LiteDB in Xamarin.Forms. What is the best practice for getting list of objects from a table using list of ids or indexes in condition?
Currently, it looks for me like this:
_db.GetCollection<T>().FindAll().Where(q => listValues.Contains(Convert.ToInt32(q.GetProperty(idColumnName))));
listValues - list of searched ids.
idColumnName - column with indexes.
But FindAll retrives all records from LiteDB. Is there any more efficint options without full scanning?
Use the query in the Find method instead which will only retrieve entries based on your query rather than the full data set. This, according to the LiteDB's guidance, is more efficient than Linq queries on the full data returned: https://github.com/mbdavid/LiteDB/wiki/Queries
So your query would look like as follows
_d.GetCollection<T>().Find(q => listValues.Contains(Convert.ToInt32(q.GetProperty(idColumnName))))
I think you can just use collection.Query().Where("Column", 1,2,3) for this
I wanted to run a query, "Find me the item with smallest 'id' which is larger than some number" ?
Is it possible in dynamodb ?
And how to do it ?
Thanks in advance.
As you probably know, a DynamoDB table can have 2 types of keys: hash keys, or hash+range keys
When you run a query, you need to specify the hash key for the item that you are looking for. If your table has a key of type hash+range, you will automatically get the results back with the range attribute sorted. Your Query request can also optionally add a KeyCondition on the range attribute so that you can require that it be larger than some number. So, yes, what you are looking for is possible, assuming that you design your table appropriately.
For more info, check out the following links:
http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html
http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/QueryAndScan.html