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A number of algorithms e.g. HRJN (Hash Rank Join:https://cs.uwaterloo.ca/~ilyas/papers/rank_join2.pdf) have been proposed in relational databases for ranking and retrieving top-K results. Does any open source relational database like postgresql implement such algorithm by default (If yes what is the database name?).
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I have two databases one in PostgreSQL and other in MySQL. What I want is to get data from both databases and create a view and then iterate it on front-end.
Is it possible?.
The smartest thing to do would be to create two connections, one to each database, and handle it that way.
If you need to join the tables, you could consider using a mysql_fdw foreign table in PostgreSQL and join the tables in PostgreSQL.
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What is nvarchar2 in sql or MySQL
It is a data type used to store string values up to 16 bits long.
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I struggle with a MySQL Join.
These are my tables:
user(id, name,...);
aim(id, title,...);
aim2user(userID, aimID);
A user can have multiple aims.
I would like to return all aims which are NOT selectet by user X.
How is this possible?
select id from aim where id not in (select zeildID from aim2user where userID=X)
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Im curious what is the distinct use of pivot table in database? I mean, how is it apply in real life.
Pivot query help us to generate an interactive table that quickly combines and compares large amounts of data. We can rotate its rows and columns to see different summaries of the source data, and we can display the details for areas of interest at a glance. It also help us to generate Multidimensional reporting.
for more information visit:
http://www.codeproject.com/Tips/500811/Simple-Way-To-Use-Pivot-In-SQL-Query
https://technet.microsoft.com/en-us/library/ms177410(v=sql.105).aspx
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how to load mysql table to memorystream with delphi? If possible; making select * from table where ?=? will be very fast. but how?
If you have FireDAC, you could use LocalSQL to write a SQL query against any TDataSet descendent, including an in memory TClientDataSet or FDMemTable.
It's explained in the documentation, and there is a webinar from the author of FireDAC demonstrating how to do it.