What is Extract/Transform/Load (ETL)?

I've tried reading the Wikipedia开发者_如何学运维 article for "extract, transform, load", but that just leaves me more confused...

Can someone explain what ETL is, and how it is actually done?

ETL is taking data from one system (extract), modifying it (transform) and loading it into another system (load).

And not necessarily in that order. You can TEL, or ELT. Probably not LTE though. :-)

It's a catch-all name for any process that takes data from one system and moves it to another.

ETL is commonly used for data warehousing. It's not a specific implementation to load a data warehouse, it's just a very high-level algorithm that should be used to populate a data warehouse.

• Extract pulls data from some source.
• Transform takes the data and manipulates it so that it can be used for..
• Loading into your system.

My favorite answer: https://stackoverflow.com/questions/51198/what-etl-tool-do-you-use/67784#67784

post removed but still at: https://web.archive.org/web/20100914194931/https://stackoverflow.com/questions/51198/what-etl-tool-do-you-use

from here

Extract means to take data out of one or many databases. Transform means to change the data however you need it changed to suit the needs of your business. Load means to put it in the target database.

ETL is short for extract, transform, load, three database functions that are combined into one tool to pull data out of one database and place it into another database. Extract is the process of reading data from a database. Transform is the process of converting the extracted data from its previous form into the form it needs to be in so that it can be placed into another database. Transformation occurs by using rules or lookup tables or by combining the data with other data. Load is the process of writing the data into the target database. ETL is used to migrate data from one database to another, to form data marts and data warehouses and also to convert databases from one format or type to another.