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dplyr is an R package whose set of functions are designed to enable dataframe (a spreadsheet-like data structure) manipulation in an intuitive, user-friendly way. It is one of the core packages of the popular tidyverse set of packages in the R programming language. [1]
A subset may be defined for deletion using a condition, otherwise all records are removed. [1] Some database management systems (DBMSs), like MySQL, allow deletion of rows from multiple tables with one DELETE statement (this is sometimes called multi-table DELETE).
A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
The relational algebra uses set union, set difference, and Cartesian product from set theory, and adds additional constraints to these operators to create new ones.. For set union and set difference, the two relations involved must be union-compatible—that is, the two relations must have the same set of attributes.
It is also possible to specify DRI actions on UPDATE and DELETE, such as CASCADE (forwards a change/delete in the referenced table to the referencing tables), NO ACTION (if the specific row is referenced, changing the key is not allowed) or SET NULL / SET DEFAULT (a changed/deleted key in the referenced table results in setting the referencing ...
In computer programming, create, read, update, and delete (CRUD) are the four basic operations (actions) of persistent storage. [1] CRUD is also sometimes used to describe user interface conventions that facilitate viewing, searching, and changing information using computer-based forms and reports .
A relation can always be decomposed in third normal form, that is, the relation R is rewritten to projections R 1, ..., R n whose join is equal to the original relation. Further, this decomposition does not lose any functional dependency , in the sense that every functional dependency on R can be derived from the functional dependencies that ...
This is also known as a Horizontal Partition, restricting rows output by a query according to specified conditions. With more than one table, the result set will be every combination of rows. So if two tables are T1 and T2, SELECT * FROM T1, T2 will result in every combination of T1 rows with every T2 rows. E.g., if T1 has 3 rows and T2 has 5 ...