Why Does My MySQL Database Throw a 'Cannot Add or Update a Child Row: a foreign key constraint fails' Error?

Foreign Key Constraint Violation: Error "Cannot Add or Update Child Row"

You've encountered a MySQL error while attempting to insert or update data in a database table, denoted by the message "Cannot add or update a child row: a foreign key constraint fails." This error occurs when you try to establish a relationship between two tables using a foreign key, but the value in the child table's foreign key column does not match a valid value in the referenced parent table.

Understanding Foreign Key Relationships

In your example, you have two tables:

• table1 with columns: UserID, Password, Username, Email
• table2 with columns: UserID, PostID,

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