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Recent questions tagged safe-query
2
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1
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safe query
Is the following query safe? Consider a database that has the relation schemas EMP(EmpId, EmpName, DeptId), and DEPT(DeptName, DeptId) 1. DEPT_ID in EMP can be null 2.DPET_ID in EMP cannot be null {t | ∃u ∈ EMP(t[EmpName] = u[EmpName] ∧ ∀v ∈ DEPT(t[DeptId] == v[DeptId]))}
Is the following query safe?Consider a database that has the relation schemas EMP(EmpId, EmpName, DeptId), and DEPT(DeptName, DeptId)1. DEPT_ID in EMP can be null2.DPET_I...
Warlock lord
1.1k
views
Warlock lord
asked
Jan 19, 2018
Databases
safe-query
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3
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0
answers
2
safe query
Is the query below safe? {t | ∃u ∈ EMP(t[EmpName] = u[EmpName] ∧ ∀v ∈ DEPT(t[DeptId] == v[DeptId]))} Please explain why.
Is the query below safe? {t | ∃u ∈ EMP(t[EmpName] = u[EmpName] ∧ ∀v ∈ DEPT(t[DeptId] == v[DeptId]))}Please explain why.
Warlock lord
1.0k
views
Warlock lord
asked
Jan 19, 2018
Databases
databases
sql
safe-query
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–
54
votes
5
answers
3
GATE CSE 2017 Set 1 | Question: 41
Consider a database that has the relation schemas EMP(EmpId, EmpName, DeptId), and DEPT(DeptName, DeptId). Note that the DeptId can be permitted to be NULL in the relation EMP. Consider the following queries on the database expressed in tuple relational calculus. { ... Which of the above queries are safe? I and II only I and III only II and III only I, II and III
Consider a database that has the relation schemas EMP(EmpId, EmpName, DeptId), and DEPT(DeptName, DeptId). Note that the DeptId can be permitted to be NULL in the relatio...
Arjun
25.1k
views
Arjun
asked
Feb 14, 2017
Databases
gatecse-2017-set1
databases
relational-calculus
safe-query
normal
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