CRUD applications to update MYSQL database

Constraints are put on a database to protect the data.

Why should you be able to delete an invoice if it belongs to an exsiting customer and is out standing?

Constraints was probably a poor choice of wording, although ironically i am also having problem with column check constraints in mariadb 10. I setup some basic column constraints while the dbase was in access that imported in perfectly, now i am finding that mariadb rejects virtually any call for a new column check constraint. Perhaps I will have to go back into MYSQL workbench to see if it can overcome the syntax gap. I have tried many variations of syntax using the case statement and then fell back to a simple check statement. I am having no trouble with the tables, queries at all. 
I have got the basic crud application to work for all phases of user registration. I have also succeeded in setting up a more advanced crud authored by alex lancer with admin lte. My base website traverses all links, using bootstrap. The challenge i didn't expect was that i would have to do joins within the controllers for the crud to gain permission to update, delete. Customization seemingly puts my built in security at risk. The parent/child error is currently at issue on my most recent crud in a new table.  I intend to try a left join to resolve crud refusing to update a table with a foreign key next. I think i have found such a crud project to follow.