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Questions and Answers
Which attribute is commonly used as a primary key in a database relation?
Which attribute is commonly used as a primary key in a database relation?
- Department
- Street
- Name
- Id (correct)
Why can 'Street' not be considered as a primary key?
Why can 'Street' not be considered as a primary key?
- It is a numerical value
- It uniquely identifies each tuple
- It is a common attribute
- It can occur more than once (correct)
What is the role of a foreign key in a relation?
What is the role of a foreign key in a relation?
- To calculate aggregate functions
- To ensure uniqueness of values
- To sort the relation
- To reference the primary key of another relation (correct)
Which term is used for the relation that contains the primary key from another relation as a normal attribute?
Which term is used for the relation that contains the primary key from another relation as a normal attribute?
What makes an attribute suitable to be a primary key?
What makes an attribute suitable to be a primary key?
Why are attributes like 'Name' and 'Street' not ideal choices for primary keys?
Why are attributes like 'Name' and 'Street' not ideal choices for primary keys?
In the given SQL query, what is the missing keyword that needs to be inserted to correctly insert values into the table?
In the given SQL query, what is the missing keyword that needs to be inserted to correctly insert values into the table?
Which of the following SQL queries does not specify the relation from which the values are selected?
Which of the following SQL queries does not specify the relation from which the values are selected?
Which keyword is essential in an SQL query to specify the table into which values need to be inserted?
Which keyword is essential in an SQL query to specify the table into which values need to be inserted?
If you want to select only the 'empid' from the 'emp' table where 'lastname' is 'GELLER', which SQL query should you use?
If you want to select only the 'empid' from the 'emp' table where 'lastname' is 'GELLER', which SQL query should you use?
What clause is missing in the following SQL query that causes it to be incorrect: 'Select * from empid = 10003;'?
What clause is missing in the following SQL query that causes it to be incorrect: 'Select * from empid = 10003;'?
Which keyword is necessary in an SQL query to indicate the condition for selecting specific records?
Which keyword is necessary in an SQL query to indicate the condition for selecting specific records?
To prevent cascading of authorizations from the user, which statement should be used?
To prevent cascading of authorizations from the user, which statement should be used?
How can confusion arising from the revoking of user roles be overcome?
How can confusion arising from the revoking of user roles be overcome?
Which keyword can be used to indicate that revocation should cascade?
Which keyword can be used to indicate that revocation should cascade?
What should be done before executing 'set role name' to associate a current role with a session?
What should be done before executing 'set role name' to associate a current role with a session?
In the context of database authorizations, what does 'revoking with restrict' prevent?
In the context of database authorizations, what does 'revoking with restrict' prevent?
What is the purpose of granting and revoking roles by the user in a database management system?
What is the purpose of granting and revoking roles by the user in a database management system?
What does the tuple relational calculus describe?
What does the tuple relational calculus describe?
In tuple relational calculus, what does the symbol ∧ represent?
In tuple relational calculus, what does the symbol ∧ represent?
Which query finds the names of all instructors whose department is in the Watson building?
Which query finds the names of all instructors whose department is in the Watson building?
Which symbol is used in place of 'except' in relational calculus?
Which symbol is used in place of 'except' in relational calculus?
What does the symbol ∀ represent in SQL?
What does the symbol ∀ represent in SQL?
Given the sentence 'Find all students who have taken all courses offered in the Biology department', which expression matches this query?
Given the sentence 'Find all students who have taken all courses offered in the Biology department', which expression matches this query?
What privilege is granted in the statement 'Grant update(budget) on department to Raj'?
What privilege is granted in the statement 'Grant update(budget) on department to Raj'?
How can privileges be removed from a user in a database management system?
How can privileges be removed from a user in a database management system?
Which role creation and authorization statement is correct to provide delete authorization to an instructor?
Which role creation and authorization statement is correct to provide delete authorization to an instructor?
In a database management system, which statement is used to provide privilege to only a particular attribute?
In a database management system, which statement is used to provide privilege to only a particular attribute?
What is the key aspect in creating views in a database management system?
What is the key aspect in creating views in a database management system?
Which statement accurately reflects the process of removing privileges from a user?
Which statement accurately reflects the process of removing privileges from a user?
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Study Notes
Privileges and Roles
- The
revokestatement can be used withrestrictto prevent cascading revocation, or withcascadeto indicate that revocation should cascade. - To avoid confusion when revoking a role, the privilege must be granted only by roles.
Tuple Relational Calculus
- A query in the tuple relational calculus is expressed as
{t | P(t)}. - This query language describes the desired information without giving a specific procedure for obtaining that information.
Queries
- The query
{t | Э s ε instructor (t[name] = s[name] ∧ Э u ε department (u[dept name] = s[dept name] ∧ u[building] = “Watson”))}finds the names of all instructors whose department is in the Watson building. - The symbol
¬is used in the place of "except". - The expression
∀ t ε r (Q(t))matches the sentence "Find all students who have taken all courses offered in the Biology department." ∀is used to denote "for all" in SQL.
Keys
- A primary key is a constraint that specifies uniqueness.
- An attribute can be taken as a primary key if it is unique for each tuple.
- A foreign key is an attribute in a relation that refers to the primary key of another relation.
- The primary key has to be referred to in another relation to form a foreign key in that relation.
Relations
- A referenced relation is the one in which the primary key of one relation is used as a normal attribute in another relation.
SQL Queries
- A query must have a
fromclause to specify the relation from which the values have to be selected. - The
insert intostatement requires thevalueskeyword to insert values into a table.
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