Keys in dbms(UNIT 2)
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This document defines and describes several key concepts in database management systems including primary keys, candidate keys, super keys, foreign keys, alternate keys, and composite keys. A primary key uniquely identifies each record in a table and can only include one column. Candidate keys can also uniquely identify records but a table can have multiple candidate keys whereas only one can be designated the primary key. Super keys may contain multiple attributes to uniquely identify records. Foreign keys link data between tables, and alternate and composite keys are secondary candidate keys that can include multiple columns to uniquely identify records.
Keys in dbms(UNIT 2)
- 1. KEYS IN DBMS BY:SURBHI SAROHA
- 2. KEYS Primary Key Candidate Key Super Key Foreign Key Alternate Key Composite Key
- 3. PRIMARY KEY A primary key, also called a primary keyword, is a column in a relational database table that's distinctive for each record. It's a unique identifier, such as a driver's license number, telephone number with area code or vehicle identification number (VIN). A relational database must have only one primary key.
- 4. CANDIDATE KEY A candidate key is a set of one or more columns that can uniquely identify a row within a table, while a primary key is a candidate key that is chosen to be the official unique identifier for a row within the table. A table can have multiple candidate keys, but can only have one primary key.
- 5. SUPER KEY Super key is a single key or a group of multiple keys that can uniquely identify tuples in a table. Super Key can contain multiple attributes that might not be able to identify tuples in a table independently, but when grouped with certain keys, they can identify tuples uniquely.
- 6. FOREIGN KEY A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables to control the data that can be stored in the foreign key table.
- 7. ALTERNATE KEY An alternate key is the secondary candidate key that contains all the property of a candidate key but is an alternate option.
- 8. COMPOSITE KEY In database design, a composite key is a candidate key that consists of two or more attributes (table columns) that together uniquely identify an entity occurrence (table row).
- 9. THANK YOU