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Marianna [84]
2 years ago
6

Short notes on primary key​

Computers and Technology
1 answer:
Thepotemich [5.8K]2 years ago
5 0

Answer:

A primary key is a special relational database table column (or combination of columns) designated to uniquely identify each table record. A primary key is used as a unique identifier to quickly parse data within the table. A table cannot have more than one primary key.

Primary Key.

Candidate Key.

Alternate Key.

Super Key.

Composite Key.

Foreign Key.

Unique Key.

In the relational model of databases, a primary key is a specific choice of a minimal set of attributes that uniquely specify a tuple in a relation. Informally, a primary key is "which attributes identify a record," and in simple cases constitute a single attribute: a unique ID.

Explanation:

You might be interested in
The automated key distribution approach provides the flexibility and dynamic characteristics needed to allow a number of users t
docker41 [41]

Answer:

The correct answer is option A. "True".

Explanation:

Key management could either be manual or automated. The automated key distribution approach is more flexible and dynamic than the manual key distribution approach, because it is better at responding to changing requirements in the system. Additionally, the automated key distribution approach is faster and more economic as well as observable and auditable.

6 0
3 years ago
¿por que la toria de lamarck sobre el alargamiento del cuello de las jirafas por el esfuerzo continuado no pasara a sus descendi
Paha777 [63]

Respuesta: Los caracteres adquiridos no se transmiten genéticamente porque no modifican el ADN de los organismos

Explicación:

Jean-Baptiste Lamarck al igual que Charles Darwin, propuso una teoría sobre la evolución que explicaba cambios en los organismos a través del tiempo. La teoría de Lamarck se enfocaba en condiciones en el ambiente que propiciaban cambios en los organismos. Un ejemplo de esto son las jirafas, que de acurdo a Lamarck tenían cuellos largos debido al esfuerzo continuado para comer hojas de árboles altos. Esto significa que la característica de cuello largo era adquirido por las jirafas durante su vida y según Lamarck se transmitiría a sus descendientes.

Sin embargo, se ha comprobado que los caracteres adquiridos no modifican el ADN de los organismos, por ejemplo las cirugías estéticas no cambian el ADN de una persona y por esta razón no son transmitidos a sus descendientes. Por el contrario, en las poblaciones de organismos ciertas características prevalencen en el tiempo debido a la selección natural. Esto significa que el cuello de las jirafas es el resultado que el cuello largo sea una característica beneficiosa que ha prevalecido debido a la selección natural y no de características adquiridas que son transmitidas a descendientes.

7 0
3 years ago
The superclass Calculator contains: a protected double instance variable, accumulator, that contains the current value of the ca
yawa3891 [41]

Answer:

The following program are written in JAVA Programming Language.

//inherit the Calculator class

public class CalculatorWithMemory extends Calculator {  

   private double memory = 0.0;    //initialize double type variable

   public void save() {   //define function

       memory = accumulator;    

   }

   public void recall() {   //define function

       accumulator = memory;

   }

   public void clearMemory() {   //define function

       memory = 0;     //initialize the value

   }

   public double getMemory() {  

       return memory;    // return the value in "memory" variable

   }

}

Explanation:

Here, we inherit the property of the "Calculator" class.

Then, we define the private double type variable "memory" and assign value 0.0.

Then we set the function "save()" inside it we assign the value of "memory" in "accumulator" and close the function.

Then, we define the function "recall()" inside it we assign the value of "accumulator" in "memory" and close the function.

Then we set the function "clearMemory()" inside it we assign "memory" to 0.

After all, we set the double type function "getMemory()" inside we return the value of the "memory".

7 0
3 years ago
Declare a structure with a type name: Car containing:
OLga [1]

Answer:

C++ code is given below

Explanation:

#include <iostream>

#include <cctype>

#include <string.h>

#include <cstring>

#include <sstream>

using namespace std;

struct Car {

public:    

char reportingMark[5];    

int carNumber;

string kind;

bool loaded;

string destination;

};

void input(Car *);

void output(Car *);

int main() {

Car *T = new Car;    

input(T);

output(T);    

delete T;    

return 0;

}

void input(Car *T)

{

string str, s;

cout << " Enter the reporting mark as a 5 or less character uppercase string: ";

cin >> str;

for (int i = 0; i < str.length(); i++)

T->reportingMark[i] = toupper(str[i]);

cout << " Enter the car number: ";

cin >> T->carNumber;

cout << " Enter the kind: ";

cin >> T->kind;

cout << " Enter the loaded status as true or false: ";

cin >> s;    

istringstream(s) >> boolalpha >> T->loaded;    

if (T->loaded == true) {

cout << " Enter the destination: ";

cin.ignore();

getline(cin, T->destination);

}

else

T->destination = "NONE";    

}

void output(Car *T)

{

cout << " Reporting Mark: " << T->reportingMark;

cout << " Car Number: " << T->carNumber;    

cout << " Kind: " << T->kind;

cout << " Loaded Status: " << boolalpha << T->loaded;

cout << " Destination: " << T->destination << " ";

}

7 0
3 years ago
write a c++ program that takes a string input from the user and removes all characters except numerals also display the number o
Xelga [282]

Answer:

hi

Explanation:

5 0
3 years ago
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