Why Am I Getting 'Cannot Add or Update a Child Row: a foreign key constraint fails' Errors?

Foreign Key Constraint Violation: Understanding "Cannot Add or Update a Child Row" Errors

When attempting to manipulate data in relational databases, you may encounter errors related to foreign key constraints. One common issue is the "Cannot add or update a child row: a foreign key constraint fails" error.

This error occurs when you try to:

• Insert a row into a "child" table with a foreign key value that does not exist in the "parent" table.
• Update the foreign key value in a child row to a value that does not exist in the parent table.

Example

Consider the following tables:

table1	table2
UserID (PRI)	UserID (MUL)
Password	PostID (PRI)
Username

table1

table2

UserID (PRI)

UserID (MUL)

Password

PostID (PRI)

Username

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