I have four tables, where the data should be checked for 1st table, if doesn't exist, then should check for 2nd table and goes on...
Currently following approach can be followed
1. Have union all on the tables and find out the above based on priority (Or)
2. Run each query from the application and verify and goes one by one (Or)
3. Using CASE and NOT_EXIST option to find out the rows accordingly
Problems:
1. Problem with JPA if all columns are extracted with asterisk (*) since count(c.*)
is not supported in SQL
2. Performance and unnecessary multiple query from application which needs to be
avoided in second approach
3. Makes the query has very complex and not interested to proceed
What would be the best practice to be followed on this use case?
Thanks
Related
I am working on very large database. Due to the privacy policy I can't write the original schema but I can give an example similar to that.
Example
Let's say I have a product table. It is the main table. It had many details and for those individual details I created other tables like product_detail_1 product_detail_2 product_detail_3 upto 10. These details tables contains many different values.
Now all these tables have a foreign key which refers to the primary key in a product table. So if I want any particular data then it's very easy to retrieve once I have the key. .
Now my question is if I want to display results based on particular details then which method I should follow?
Method 1:
I run query everytime I want to search.
In this case the query will be too long because the query likely to contain 4 to 7 where clauses on different detail tables so it will take some time to execute.
OR
Method 2:
I store the result of every search query in a new table.
Benefits of this technique is
- If the same query executed again then the result is already available so it won't take much time.
So if I store query result in a table with text datatype column is there any limitations for length in column?
Or should I try method 1?
I'm using mysql database
We are building an analytics engine which has to store attribute preference score for each user. We are expecting 400 attributes and they may change(at what frequency is not known as yet). We are planning to store this in Redshift.
My qs is:
Should we store as 1 row per user with 400 cols(1 column for each attribute)
or should we go for a table structure like
(uid, attribute id, attribute value, preference score) which will be (20-400)rows by 3 columns
Which kind of storage would lead to a better performance in Redshift.
Should be really consider NoSQL for this?
Note:
1. This is a backend for real time application with increasing number of users.
2. For processing, the above table has to be read with entire information of all attibutes for one user i.e indirectly create a 1*400 matrix at runtime.
Please help me which desgin would be ideal for such a use case. Thank you
You can go for tables like given in this example and then use bitwise functions
http://docs.aws.amazon.com/redshift/latest/dg/r_bitwise_examples.html
Bitwise functions are here
For your problem, I would suggest a two table design. Its more pain in the beginning but will help in future.
First table would be a key value kind of first table, which would store all the base data and would be kind of future proof, where you can add/remove more attributes, but this table will continue working.
And a N(400 in your case) column 2nd table. This second table you can build using the first table. For the second table, you can start with a bare minimum set of columns .. lets say only 50 out of those 400. So that querying this table would be really fast. And the structure of this table can be refreshed periodically to match with the current reporting requirements. Also you will always have the base table in case you need to backfill any data.
I basically have results grid and i have a drop down menu on my application which filters the 'Carrier' column. But when selecting a certain carrier I want all the rows returned that have the same dr_id as the Carrier which has been selected.
For example if you look at the picture attached it shows my results grid. If I filter by carrier 'ACE CALL LTD_UK' then I want rows 27, 28, 29 and 30 returned because the dr_id is the same.
Thanks
I don't have a complete solution for you as I don't know exactly what you database schema is (and it is a large stored procedure!). However I do have some suggestions/comments which you might find helpful:
I assume that the stored procedure will currently be returning a single row when they filter is set to 'ACE CALL LTD_UK', if not then this might not be relevant!
What I would do in this case would be to take you SELECT statement and put the results into a CTE, temporary table or nested query. (I'm not sure what SQL DBMS your using, looks like MSSQL, but you also have a MySQL tag for you post).
Once I have those results I would then use a LEFT JOIN from the dr_id in the temp table back to the drm table on the same column. From here you will again need to join to other tables where the data is not distinct, for example the Carrier table, then select the columns that you require.
You could do all this in the existing SELECT statement, however you will have to start joining on tables multiple times or use nested queries, which would get very messy. However the main reason why I chose the solution I have posted is because I don't know the stored procedure well enough and therefore I chose the safest solution.
If you want an example of what I mean, I will try and provide one.
I am trying to use the results of another query to use as a criteria for another. In my specific example, I might have four houses that are 'A', 'B', 'C', 'D' (the unique values of a field in a table called Homes).
I want to go through another query and say for each house type, what percent of residents (in Residents table) are married, which I want to do by using Count() to count the number for each Home type.
Do I need to loop through the results using VBA? Asking on a higher level, is there a way to use the results from a query as inputs into another - more than just limit the results of the new query to the results of the prior query?
Edit:
In semi-pseudo code:
For each (result of previous query) Do
New query WHERE field1 = (row of previous query)
End Do
What I am trying to ask, is there a way to accomplish this in Access using SQL? Or is this something that has to be done in VBA?
I know that if it can be done in SQL that would be the best performing and best practice, but I'm relatively inexperienced in SQL and online resources aren't always helpful because Access has it's own particular flavor of SQL.
Since you are using VBA to run this, you can loop through your recordsets and yes you can use a value from one query in the next query. There are alot of resources out there to help.
VBA: Working with RecordSets
Looping through Record Sets
Code through all records
To answer your general question, yes there is. You can do a nested query i.e. select column a from table a where column a = (select column b from table b where column b=x)
You can go as many levels deep as you want, but the caveat is the nested query can only return one column and with a specific answer set. You can also use select statements as your columns i.e
select (select column b from table b) col b from table a ..... Not the exact syntax but I would have to dig out some examples from an old project to find that.
Nested queries are useful, but for the level of precision you are looking for, a stored procedure or a view is probably a better option. Just for ease of use, I would look at creating a view of the data that you want and then querying from that to start with. More flexible than a nested query.
You need to join two tables using a common column and then get your specific column from any of the table
SELECT A.REQUIRED_FIELD from TABLEA AS A
INNER JOIN TABLEB AS B ON A.FOREIGN_KEY=B.FOREIGN_KEY
WHERE CONDITION
I have two tables, that is joined in some way. I've spent the last hour googling around, not finding any concrete answers that worked in my case.
The case is, table 1 is called Clients, and table 2 is called Projects. I need to list all the client names, followed by number of projects related to that project and the project title.
For example:
Client 1 (2 projects)
- Project 1 title
- Project 2 title
Client 2 (0 projects)
Client 3 (1 project)
- Project 1 title
How is this doable, in the simplest and easiest way?
There are basically three parts to your query.
Joining the tables
Grouping the output by project
Counting the projects per client
The first is easy. It involves finding the client ID field in each table and use an JOIN clause specifying the two columns (one in each table) to correlate on. This will give you one row per project that also contains information for the matching client. This is almost what you're asking for.
It is tricky to put the second and third together in the one query and not one I would recommend. If you are going to be putting this in a program, then you can easily post-process the result from the query. To do this, you need to add an ORDER BY clause to specify sorting by client. That will put all the projects for each client in subsequent rows.
Now you can write a loop to process the output. As it does to, it has to watch for two things:
when the client ID changes
counting the projects
By doing this, it can easily display a "group header" for each client, and a "group footer" for the number of projects.
You don't say anything about your app, but I'd recommend separating querying from displaying. Let SQL get the data for you and then let something else do presentation.