The number of attributes in a relation is known as its:
- A.Cardinality
- B.Degree
- C.Domain
- D.Tuple count
Correct answer
Explanation
The correct answer is B, degree. The degree of a relation counts its attributes, that is its columns, so a student table holding roll number, name, class and marks has degree four whatever the number of students in it. Option A is wrong because cardinality counts the tuples, that is the rows of the table, so the same student table with two hundred students has cardinality two hundred. Option C is wrong because a domain is the set of permitted values for one attribute, for example the letters A to E for a grade column, and it is not a count at all. Option D is wrong because tuple count is only another name for cardinality, so it repeats the error in option A. Examiners frequently swap degree and cardinality in the options, so read the words attribute and tuple carefully before choosing.
Read the full article: Databases and DBMS: Models, Keys, SQL and Normalisation
Practice Questions
View allWhich of the following is the oldest database model?
- A.Hierarchical
- B.Object oriented
- C.Deductive
- D.Relational
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The hierarchical model is the first data model used in commercial database software; IBM built its Information Management System on it in the 1960s for the Apollo programme.
Read the full explanation →Who proposed the relational model of databases?
- A.Charles Babbage
- B.Edgar Frank Codd
- C.Dennis Ritchie
- D.James Gosling
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Codd, a British computer scientist working at IBM, set out the relational model in a paper published in 1970, proposing that all data be held in simple two-dimensional tables and joined by matching values rather than by fixed pointers.
Read the full explanation →In relational database terminology, a row of a table is called a:
- A.Attribute
- B.Domain
- C.Tuple
- D.Relation
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In the vocabulary of the relational model a table is a relation, and one complete horizontal entry of that table, such as all the details of a single student, is a tuple; the ordinary words for it are row and record.
Read the full explanation →Which of the following is a Data Definition Language (DDL) command in SQL?
- A.INSERT
- B.CREATE
- C.SELECT
- D.UPDATE
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The Data Definition Language deals with the structure of the database rather than with the data inside it, and CREATE is its basic command, used to build a table, a view or the database itself; ALTER, DROP, TRUNCATE and RENAME belong to the same group.
Read the full explanation →Which SQL command removes all the rows of a table but keeps the table structure, and is classified as a DDL command?
- A.DELETE
- B.DROP
- C.TRUNCATE
- D.ERASE
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TRUNCATE empties a table in one operation, leaving the columns, data types and constraints in place so that the table can be filled again at once; because it changes the object rather than selected rows it is grouped with the Data Definition Language and it is much faster than deleting…
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