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Hi/Lo is an algorithm and a key generation strategy used for generating unique keys for use in a database as a primary key.It uses a sequence-based hi-lo pattern to generate values.
Key Name Definition Simple A key made from only one attribute. Concatenated A key made from more than one attribute joined together as a single key, such as part or whole name with a system generated number appended as often used for E-mail addresses. Compound: A key made from at least two attributes or simple keys, only simple keys exist in a ...
A candidate key, or simply a key, of a relational database is any set of columns that have a unique combination of values in each row, with the additional constraint that removing any column could produce duplicate combinations of values. A candidate key is a minimal superkey, [1] i.e., a superkey that does not contain a smaller one. Therefore ...
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 ...
A surrogate key is frequently a sequential number (e.g. a Sybase or SQL Server "identity column", a PostgreSQL or Informix serial, an Oracle or SQL Server SEQUENCE or a column defined with AUTO_INCREMENT in MySQL). Some databases provide UUID/GUID as a possible data type for surrogate keys (e.g. PostgreSQL UUID [3] or SQL Server ...
&name; where name is the case-sensitive name of the entity. The semicolon is required. Because numbers are harder for humans to remember than names, character entity references are most often written by humans, while numeric character references are most often produced by computer programs. [1]
Next to this name, a character can have one or more formal (normative) alias names. Such an alias name also follows the rules of a name: characters used (A-Z, -, 0-9, <space>) and not used (a-z, %, $, etc.). Alias names are also unique in the full name set (that is, all names and alias names are all unique in their combined set).
The heading defines a set of attributes, each with a name and data type (sometimes called a domain). The number of attributes in this set is the relation's degree or arity. The body is a set of tuples. A tuple is a collection of n values, where n is the relation's degree, and each value in the tuple corresponds to a unique attribute. [6]