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Questions and Answers
What is a superkey in the context of relational databases?
What is a superkey in the context of relational databases?
- A set of all attributes in a relation that specifies no two tuples can have the same value (correct)
- A procedural query language for relational databases
- A set of attributes that uniquely identify the tuples in a relation
- A constraint that specifies whether null values are permitted or not
What is the purpose of the entity integrity constraints in relational databases?
What is the purpose of the entity integrity constraints in relational databases?
- To declare primary keys for the entities
- To operate on pairs of relationships using binary operations
- To specify that no primary key value can be null (correct)
- To create a table for each entity
What is the function of the select operation in relational algebra?
What is the function of the select operation in relational algebra?
- Specifying whether null values are permitted or not
- Declaring primary keys for the entities
- Selecting tuples that satisfy a given predicate (correct)
- Creating a table for each entity
What is the DEGREE OF A RELATION?
What is the DEGREE OF A RELATION?
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Which type of constraint is DOMAIN CONSTRAINTS?
Which type of constraint is DOMAIN CONSTRAINTS?
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What is the purpose of KEY CONSTRAINTS?
What is the purpose of KEY CONSTRAINTS?
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What does SQL stand for?
What does SQL stand for?
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Which SQL component is used to modify database schema?
Which SQL component is used to modify database schema?
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What is the purpose of Cartesian product in SQL?
What is the purpose of Cartesian product in SQL?
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Which SQL keyword is used to delete data from a database?
Which SQL keyword is used to delete data from a database?
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Study Notes
Relational Databases
- A superkey is a set of attributes that uniquely identifies a tuple in a relation.
- Entity integrity constraints ensure that each tuple in a relation has a unique value for the primary key.
Relational Algebra
- The select operation is used to select a subset of tuples from a relation that satisfies a given condition.
Relations
- The degree of a relation is the number of attributes in a relation.
Constraints
- Domain constraints are constraints that apply to a single attribute or column of a relation, restricting the set of values it can take.
- Key constraints are used to ensure that each tuple in a relation has a unique value for the primary key.
SQL
- SQL stands for Structured Query Language.
- The DDL (Data Definition Language) component of SQL is used to modify the database schema.
- The Cartesian product operation in SQL is used to combine each row of one relation with each row of another relation.
- The DELETE keyword is used to delete data from a database.
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