this is a badly set up page and a badly set up database.
it looks like you are trying to store it looks like your select list is a multiple select list which would mean that projects are stored as a comma separated list to the database.
this is a bad practice. this is not the correct way to create a many to many relationship
your project categories should be in it;s own table:
categorieID - primary key
categoriesName - varchar
the categories table should be used to populate the list.
Should the category select list be a multiple select List? or should a project belong to only 1 category?
If the project should belong to only 1 category, then you can use a standard insert to the products table, and store the category ID.
if a project can belong to more than 1 category, then you are trying to create a many to many relationship, and will need a 3rd linking table:
projectcategorieID - primary key
projectcategorieProjectID - relates to project.id
projectcategorieCategoryID - relates to categories.categorieID
and you will need to use the manage relational table behavior to assign the categories to projects.