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Most data integration tools skew towards ETL, while ELT is popular in database and data warehouse appliances. Similarly, it is possible to perform TEL (Transform, Extract, Load) where data is first transformed on a blockchain (as a way of recording changes to data, e.g., token burning) before extracting and loading into another data store. [14]
Data mining, discovery of patterns in large data sets using statistics, database knowledge or machine learning; Data retrieval, obtaining data from a database management system, often using a query with a set of criteria; Extract, transform, load (ETL), procedure for copying data from one or more sources, transforming the data at the source ...
A relational database organizes data into one or more data tables in which data may be related to each other; these relations help structure the data. SQL is a language that programmers use to create, modify and extract data from the relational database, as well as control user access to the database.
Wikipedia preprocessor (wikiprep.pl) is a Perl script that preprocesses raw XML dumps and builds link tables, category hierarchies, collects anchor text for each article etc. Wikipedia SQL dump parser is a .NET library to read MySQL dumps without the need to use MySQL database; WikiDumpParser – a .NET Core library to parse the database dumps.
A SELECT statement retrieves zero or more rows from one or more database tables or database views. In most applications, SELECT is the most commonly used data manipulation language (DML) command. As SQL is a declarative programming language, SELECT queries specify a result set, but do not specify how to calculate it.
A derived table is the use of referencing an SQL subquery in a FROM clause. Essentially, the derived table is a subquery that can be selected from or joined to. The derived table functionality allows the user to reference the subquery as a table. The derived table is sometimes referred to as an inline view or a subselect.
In order to retrieve the desired data the user presents a set of criteria by a query. Then the database management system selects the demanded data from the database. The retrieved data may be stored in a file, printed, or viewed on the screen. A query language, like for example Structured Query Language (SQL), is used to prepare the queries.
The Python pandas software library can extract tables from HTML webpages via its read_html() function. More challenging is table extraction from PDFs or scanned images, where there usually is no table-specific machine readable markup. [1] Systems that extract data from tables in scientific PDFs have been described. [2] [3]