Combining multiple data points into a single data point. This usually is used in reference to SQL and usually to an aggregate function of some sort.

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6
votes
2answers
951 views

Using totals on aggregates to improve performance

I have two tables: details and totals of these details. Details (Slow solution): select OrderId = r.OrderId , TotalQty = SUM(r.Quantity) , ...
8
votes
5answers
14k views

How can I use a default value in a Select query in PostgreSQL?

I would like to use a default value for a column that should be used if no rows is returned. Is that possible in PostgreSQL? How can I do it? Or is there any other way I can solve this? E.g. ...
6
votes
2answers
584 views

Most efficient way to return multiple aggregates in a single stored proc?

What is the best or most efficient way to get multiple aggregate result values? Basically I have an email app and wanted to get all the numbers of messages for each type of folder (inbox, sent, ...
41
votes
4answers
10k views

What is the difference between select count(*) and select count(any_non_null_column)?

I seem to remember that (on Oracle) there is a difference between uttering select count(*) from any_table and select count(any_non_null_column) from any_table. What are the differences between these ...
4
votes
2answers
472 views

MAX for each subset

I have a table that looks like this: +---------------------------------------------+ | EVENT_ID | ITEM_ID | PERSON_ID | EVENT_DATE | +---------------------------------------------+ | 123 | 1 ...
4
votes
1answer
2k views

How do I horizontally partition an oracle database table, and should I?

We have a tenanted data warehouse that we are doing reporting on. Queries are beginning to take a long time, and we're looking at options to reduce this. There are two thoughts at the moment. Create ...
17
votes
10answers
36k views

Eliminate duplicates in ListAgg (Oracle)

Prior to Oracle 11.2 I was using a custom aggregate function to concatenate a column into a row. 11.2 Added the LISTAGG function, so I am trying to use that instead. My problem is that I need to ...
7
votes
3answers
12k views

Calculating percentage of a row over total sum

Apologies for the bad title, I wasn't sure what would be a good title for this. This is currently (simplified view of the) data I'm working with Agent | Commission ---------|------------ ...
46
votes
4answers
5k views

Storing vs calculating aggregate values

Are there any guidelines or rules of thumb to determine when to store aggregate values and when to calculate them on the fly? For example, suppose I have widgets which users can rate (see schema ...