What is a secondary key in a database?
DEFINITION: A secondary key is made on a field that you would like to be indexed for faster searches. A table can have more than one secondary key. The main purpose of a database is to store and search for data. When databases become large, possibly with hundreds of thousands of records, they can take a while to search
A composite key, in the context of relational databases, is a combination of two or more columns in a table that can be used to uniquely identify each row in the table. Uniqueness is only guaranteed when the columns are combined; when taken individually the columns do not guarantee uniqueness.
- A primary key can be made up of one or more columns; the only requirement of the PK is that the combination of columns in it must combine to create a unique value for each row. If the primary key is defined as using more than one column, it is a composite - or concatenated - primary key.
- Compound Key. A compound key consists of more than one attribute to uniquely identify an entity occurrence. Each attribute, which makes up the key, is also a simple key in its own right. For example, we have an entity named enrolment, which holds the courses on which a student is enrolled.
- Defining Composite Primary and Foreign Keys. When you use the multiple-column constraint format, you can create a composite key. A composite key specifies multiple columns for a primary-key or foreign-key constraint. A referential constraint must have a one-to-one relationship between referencing and referenced columns
Any of the keys described before (ie: primary, secondary or foreign) may have one or more attributes. A simple key consists of a single attribute to uniquely identify an entity occurrence, for example, a student number, which uniquely identifies a particular student. No two students would have the same student number.
- A primary key, also called a primary keyword, is a key in a relational database that is unique for each record. It is a unique identifier, such as a driver license number, telephone number (including area code), or vehicle identification number (VIN). A relational database must always have one and only one primary key.
- Simple Key-Management for Internet Protocol or SKIP was a protocol developed circa 1995 by the IETF Security Working Group for the sharing of encryption keys. Therefore, no connection setup overhead exists and new keys values are not continually generated.
- Ike Broflovski
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Updated: 2nd October 2019