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In the relational model of databases, a primary key is a designated attribute that can reliably identify and distinguish between each individual record in a table.The database creator can choose an existing unique attribute or combination of attributes from the table (a natural key) to act as its primary key, or create a new attribute containing a unique ID that exists solely for this purpose ...
If there is more than one extended partition in a partition table, only the logical drives in the first recognized extended partition type are processed. Some late versions of the DR-DOS IBMBIO.COM provide a preboot config structure, holding bit flags to select (beside others) between various drive letter assignment strategies.
The device mapper is a framework provided by the Linux kernel for mapping physical block devices onto higher-level virtual block devices.It forms the foundation of the logical volume manager (LVM), software RAIDs and dm-crypt disk encryption, and offers additional features such as file system snapshots.
In this case the logical primary key for AB is formed from the two foreign keys (i.e. copies of the primary keys of A and B). In web application frameworks such as CakePHP and Ruby on Rails, a many-to-many relationship between entity types represented by logical model database tables is sometimes referred to as a HasAndBelongsToMany (HABTM ...
The Linux-IO Target (LIO) is an open-source Small Computer System Interface (SCSI) target implementation included with the Linux kernel. [ 1 ] [ better source needed ] Unlike initiators, which begin sessions, LIO functions as a target, presenting one or more Logical Unit Numbers (LUNs) to a SCSI initiator , receiving SCSI commands, and managing ...
Logical block addressing (LBA) is a common scheme used for specifying the location of blocks of data stored on computer storage devices, generally secondary storage systems such as hard disk drives. LBA is a particularly simple linear addressing scheme; blocks are located by an integer index, with the first block being LBA 0, the second LBA 1 ...
To discover such errors, one must perform a query that uses a left outer join between the table with the foreign key and the table with the primary key, showing both key fields in addition to any fields required to distinguish the record; all invalid foreign-key values will have the primary-key column as NULL. The need to perform such a check ...
Conjunctive queries without distinguished variables are called boolean conjunctive queries.Conjunctive queries where all variables are distinguished (and no variables are bound) are called equi-join queries, [1] because they are the equivalent, in the relational calculus, of the equi-join queries in the relational algebra (when selecting all columns of the result).