In a relational database design that contains a one to many 1 to N relationship between two tables, in which table is the foreign key normally placed to represent this relationship correctly?

Introduction / Context:
This question addresses a basic principle of relational database design, namely where to place the foreign key in a one to many 1 to N relationship. In such a relationship, a single row in the parent table can be associated with many rows in the child table. The foreign key is the mechanism that links each child row back to its parent. Understanding this rule is essential for producing correct and normalized database schemas.

Given Data / Assumptions:

We have two tables connected by a one to many relationship.
One table is the parent or master table on the one side.
The other table is the child or detail table on the many side.
A foreign key is required to represent the relationship in the schema.
We are choosing where the foreign key column should be placed.

Concept / Approach:
In a one to many relationship, each row in the child table must reference one row in the parent table. To accomplish this, the primary key of the parent table is copied into the child table as a foreign key. This design allows multiple child rows to point to the same parent key value, representing the many side. Placing the foreign key in the parent table would not work, because that would allow only one reference from the parent to the child, contradicting the many side requirement. Likewise, storing foreign keys in a separate table would complicate the design without providing any clear benefit.

Step-by-Step Solution:
Step 1: Identify the parent table on the one side of the relationship, which contains the primary key that other rows will reference.Step 2: Identify the child table on the many side, which can contain multiple rows associated with a single parent.Step 3: Recall that the foreign key column is a copy of the parent primary key stored in the child table.Step 4: Evaluate the options and find the one that places the foreign key in the child table.Step 5: Confirm that placing the foreign key in the child table supports the one to many relationship by allowing many child rows to reference one parent row.

Verification / Alternative check:
Consider a classic example where the parent table is Department and the child table is Employee. Each department can have many employees. The Employee table contains a DepartmentId foreign key column that references the primary key of the Department table. This setup allows multiple employees to belong to the same department, which is exactly the 1 to N pattern. If the foreign key were placed in the Department table, it could reference only a single employee, which would be incorrect. This example verifies that the correct placement is in the child table.

Why Other Options Are Wrong:
Placing the foreign key in the parent table would constrain the relationship to at most one child per parent, which violates the many side requirement. Allowing the foreign key to be in either table without recognizing parent and child roles ignores relational design rules. Storing the key in both tables introduces redundancy and potential inconsistencies. Using a separate table that stores only foreign keys complicates the schema and does not reflect standard normalization practices for simple one to many relationships.

Common Pitfalls:
Beginners sometimes misinterpret one to many notation and mistakenly place foreign keys in the wrong table, especially when naming conventions are confusing. Another pitfall is overcomplicating the design by introducing extra tables for relationships that can be represented directly with a foreign key. To avoid these issues, always identify the parent table as the one referenced by many child rows and place the foreign key in the child table. This rule is consistent across relational database systems.

Final Answer:
In a one to many relationship, the foreign key is placed in the child table that represents the many side of the relationship.