Primary key: To identify each record in a table, at least there must be one data field, which should be unique. That is corresponding data field of every record should be unique. It is called primary key. Primary key is used to identify the unique record from a collection of records. Foreign key: Sometimes, it is necessary to relate two tables to maintain some details in another table, which contains the relationship between two tables. So, to connect two tables, a primary key field in one table is added to the related table, and it is called foreign key.

Question

Problem: Having created the table structure in Problem 1, write the SQL code to enter the first two rows for the table shown in Figure P8.2. Each row should be inserted individually, without using a subquery. Insert the rows in the order that they are listed in the figure.I gor an error: RROR 1062 (23000) at line 1: Duplicate entry '101' for key 'PRIMARY' when I used this script below, I got an error. see image.ERROR 1062 (23000) at line 1: Duplicate entry '101' for key 'PRIMARY' INSERT INTO EMP_1 VALUES ('101','News','John','G','2000-11-08','502');INSERT INTO EMP_1 VALUES ('102','Senior','David','H','1989-07-12','501');

Answer 1

Question

Chapter 8, Problem 19P

Program Plan Intro

Primary key:

To identify each record in a table, at least there must be one data field, which should be unique.

That is corresponding data field of every record should be unique.

It is called primary key.

Primary key is used to identify the unique record from a collection of records.

Foreign key:

Sometimes, it is necessary to relate two tables to maintain some details in another table, which contains the relationship between two tables.

So, to connect two tables, a primary key field in one table is added to the related table, and it is called foreign key.

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Problem: Having created the table structure in Problem 1, write the SQL code to enter the first two rows for the table shown in Figure P8.2. Each row should be inserted individually, without using a subquery. Insert the rows in the order that they are listed in the figure.I gor an error: RROR 1062 (23000) at line 1: Duplicate entry '101' for key 'PRIMARY' when I used this script below, I got an error. see image.ERROR 1062 (23000) at line 1: Duplicate entry '101' for key 'PRIMARY' INSERT INTO EMP_1 VALUES ('101','News','John','G','2000-11-08','502');INSERT INTO EMP_1 VALUES ('102','Senior','David','H','1989-07-12','501');

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