MySQL 1216: Cannot delete or update a parent row.

What is MySQL 1216: Cannot delete or update a parent row.

When encountering error 1216: "Cannot delete or update a parent row" in MySQL, it indicates a foreign key constraint failure. Here are immediate actions to investigate and address the issue:

Identify the Foreign Key Constraint:

- Run the following query to identify the foreign key constraint that is causing the issue. Replace `yourtablename` with the name of the table you are trying to update or delete from.SELECT CONSTRAINTNAME, TABLENAME, COLUMNNAME, REFERENCEDTABLENAME, REFERENCEDCOLUMN_NAME FROM INFORMATIONSCHEMA.KEYCOLUMN_USAGE WHERE TABLESCHEMA = 'yourdatabasename' AND TABLENAME = 'yourtablename';

Check for Dependent Rows in the Child Table:

- Use the information obtained from step 1 to find dependent rows in the child table. Replace `childtablename`, `childcolumnname`, `parenttablename`, and `parentcolumnvalue` with the actual table and column names, and the value you tried to delete or update.SELECT * FROM childtablename WHERE childcolumnname IN (SELECT parentcolumnvalue FROM parenttablename WHERE your_condition);

Decide on Action for Dependent Rows:

- Based on the business logic, decide if you need to delete, update, or reassign these dependent rows. Here are examples for each action:Delete Dependent Rows (Caution: This will permanently remove the dependent rows):DELETE FROM childtablename WHERE childcolumnname = 'value';Update Dependent Rows (To remove the dependency before deleting/updating the parent row):UPDATE childtablename SET childcolumnname = 'newvalue' WHERE childcolumnname = 'oldvalue';Reassign Dependent Rows (To another parent row, if applicable):UPDATE childtablename SET childcolumnname = 'newparentvalue' WHERE childcolumnname = 'currentparentvalue';

Retry the Original Operation:

- After addressing the dependent rows, retry the original delete or update operation on the parent table.Ensure that each action taken is in line with your application's data integrity and business rules.