Primary Key: A Primary Key in a database table is a field in the table that uniquely identifies every row or record present in the database table. Example: Students in Universities are assigned a unique registration number. Therefore, in a STUDENT database table, the attribute “reg_no” acts as primary key. Foreign Key: Foreign Key is a column in a relational database table which provides a relation between two tables. It provides a cross reference between tables by pointing to primary key of another table. Example: In STUDENT database table, the attribute “reg_no” acts as primary key and in COURSE database table in which the student selects his or her course, the same “reg_no” acts as foreign key for the STUDENT table.

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How to develop a C program that receives the message sent by the provided program and displays the name and email included in the message on the screen?Here is the code of the program that sends the message for reference: typedef struct { long tipo; struct { char nome[50]; char email[40]; } dados;} MsgStruct; int main() { int msg_id, status; msg_id = msgget(1000, 0600 | IPC_CREAT); exit_on_error(msg_id, "Creation/Connection"); MsgStruct msg; msg.tipo = 5; strcpy(msg.dados.nome, "Pedro Silva"); strcpy(msg.dados.email, "pedro@sapo.pt"); status = msgsnd(msg_id, &msg, sizeof(msg.dados), 0); exit_on_error(status, "Send"); printf("Message sent!\n");}

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Chapter 3, Problem 3RQ

Program Plan Intro

Primary Key:

A Primary Key in a database table is a field in the table that uniquely identifies every row or record present in the database table.

Example:

Students in Universities are assigned a unique registration number. Therefore, in a STUDENT database table, the attribute “reg_no” acts as primary key.

Foreign Key:

Foreign Key is a column in a relational database table which provides a relation between two tables. It provides a cross reference between tables by pointing to primary key of another table.

Example:

In STUDENT database table, the attribute “reg_no” acts as primary key and in COURSE database table in which the student selects his or her course, the same “reg_no” acts as foreign key for the STUDENT table.

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How to develop a C program that receives the message sent by the provided program and displays the name and email included in the message on the screen?Here is the code of the program that sends the message for reference: typedef struct { long tipo; struct { char nome[50]; char email[40]; } dados;} MsgStruct; int main() { int msg_id, status; msg_id = msgget(1000, 0600 | IPC_CREAT); exit_on_error(msg_id, "Creation/Connection"); MsgStruct msg; msg.tipo = 5; strcpy(msg.dados.nome, "Pedro Silva"); strcpy(msg.dados.email, "pedro@sapo.pt"); status = msgsnd(msg_id, &msg, sizeof(msg.dados), 0); exit_on_error(status, "Send"); printf("Message sent!\n");}

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