Could someone please help me understand how to populate the fact table with Surrogate keys from dimensions using SSIS?
I load my dimension tables and assign for each a surrogate key. I want to add these surrogate keys to my fact table but I don't know from where to start.
You just join your fact source record to the relevant dimension tables and get the surrogate keys, which you then insert into your fact table
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I would like to spare some tables in my database.
One table for example has a simple Primary-Key-ID column and a VARCHAR2 column.
The VARCHAR2 column has NO duplicate values, yet different unique IDs.
The PK column of this table is just referenced once as a foreign key in another table.
My thoughts are now to insert the values from the VARCHAR2 column into the the table which has held the primary key.
I could now remove the foreign key reference, delete the table and gain a new column with all the (duplicate) VARCHAR2 values. These I would like to compress in a unique/distinct way.
I have heard about index in the Oracle Database to compress column(s) but I am not quite sure which index I need or how to use them...
The underlying feature (and storage savings) should be about as the same as it was with the previous table of unique values and the foreign key reference.
Thank you for your help in advance!
Oracle basic compression allows us to compress tables. It comes with several distinct limitations, not the least of which is that it isn't suitable for OLTP databases. Direct path inserts, updates and deletes don't benefit. So you can't do what you want that way. If your organisation has sprung for the Advanced Compression licence then you have more options, but the compression still works on the table not an individual column.
I think you've confused things with index compression, which does operate on columns, as it allows us to compress the leading column(s) of a compound index. But it's worth applying only when there's a lot of repetition in those columns. If your index has a unique ID for the leading column than compression will actually increase the total amount of space taken. (Just one reason why compound indexes should be built with the least selective column first and the most selective column last.)
Your table is a classic key-value lookup table. So you could consider converting it into an index-organized table. You would save yourself a bit of space by maintaining only a specialized index instead of a table and its primary key index. Find out more
With RDBMS we usually use a numeric columns for keys (both foreign and primary), as it allows for a better joined query performance and smaller resource usage, in most cases, than other data types (like strings).
The question is, what should be the data type of choice for the key columns in a Parquet tables? Can we go like this:
SELECT * FROM parquet_table1 JOIN parquet_table2 ON t1_string_pk = t2_string_fk
What is the best practice here?
The reason for this question is that when loading data into a data warehouse, any numeric key column (for a target table) requires a key table lookup ([source system, source key] -> surrogate key), and the string key column does not; we may use source key concatenation to get us a string surrogate key value.
I have a huge table that i am querying and i just wanted to know how do i find the composite keys of a table as this table does not have a primary key however it contains an auto incremented id.
The table looks like this :
I am a beginner to SQL so any help will be appreciated thanks.
I am using Oracle 11.2. Our usecase is like NoSQL. But still we need to persist data in Oracle. The requirement is store three columns: key, name, value.
There can be millions of key, hundreds of name, value size is about 2k~8k. Different name can have the same key value.
If I just create a table in Oracle with these three column and use Key+Name as primary key.
Is it doable to let oracle store all rows with the same key together to same key space?
If rows with the same key increase, will oracle keep these value together in physical storage?
I am wondering if a PL/SQL (oracle) table can carry three foreign keys? thanks in advance if any one can help me in this regard.
There is no explicit limit on the number of foreign keys on a table. However, there is a limit of 1000 columns per table, so that probably constitutes a practical limit.
Here is a SQL Fiddle which creates a toy table with five foreign keys.
There is not limit on foreign keys use except logic which based behind use of foreign keys, and if one table needs too much foreign keys, which is not logic wise, and database design suffers in such scenario.
As well as 1000-column constraint of oracle tables and pl/sql procedures also have limit in code.