foreign-keys

This should be a fairly straightforward question, but I'm unable to find an easy answer. How do you create a foreign key that is also a primary key in MySQL? Here's my current attempt: CREATE TABLE Sale( sale_id CHAR(40), PRIMARY KEY(sale_id), discount DOUBLE, type VARCHAR(255), price DOUBLE, ); CREATE TABLE Normal_Sale( sale_id CHAR(40), PRIMARY KEY(sale_id); ); CREATE TABLE Special_Sale( sale_id CHAR(40), PRIMARY KEY(sale_id); ); What am I missing here? Thanks in advance. Add FOREIGN KEY (sale_id) REFERENCES Sale(sale_id) to each foreign table: CREATE TABLE Sale( sale_id CHAR(40), PRIMARY

I am very confused about those two terms. Are they the same or different? Some books and people say they are the same and others say they are different. I tried but couldn't find a conclusive answer. I am supposing that you are talking about using the REFERENCES where the FOREIGN KEY keyword is not used, eg. author_id INTEGER REFERENCES author(id) ... instead of ... author_id INTEGER, FOREIGN KEY(author_id) REFERENCES author(id) The answer is, that it is simply shorthand syntax for the same thing. The main concern when altering between the two should be readability. "Reference key" isn't a

i'm having trouble configuring a foreign key relationship in my Entity Framework fluent Api: Here is the head of the report: public class Testata { public Testata() { Details = new List<Dettaglio>(); } public virtual int IDTEST { get; set; } public virtual string Value { get; set; } public virtual int IDDETAIL { get; set; } public virtual string IDTESTALT { get; set; } public virtual byte[] BLOB { get; set; } public virtual IList<Dettaglio> Details { get; set; } } This is the report's detail public class Dettaglio { public virtual int IDDETAIL { get; set; } public virtual int IDTEST { get; set

I have an error when trying to update my database after adding a migration. Here are my classes before add-migration public class Product { public Product() { } public int ProductId { get; set; } public string Name { get; set; } public decimal Price { get; set; } public bool Istaxable { get; set; } public string DefaultImage { get; set; } public IList<Feature> Features { get; set; } public IList<Descriptor> Descriptors { get; set; } public IList<Image> Images { get; set; } public IList<Category> Categories { get; set; } } public class Feature { public int Id { get; set; } public string Title {

I have products belonging to collections. A collection is just a name. Products have a collection_id. In my _form view that is used for creation and edition of products, i'd like to have a drop down menu with the name of all collection. Problem, it seems there is no select method affiliated to form.for and i am trying to use : select(method, choices, options = {}, html_options = {}) from the doc but i do not understand it. I must write a methode to create a form? What are the choices, and the 2 options? Two parameters should be enough to populate an < option> tag. How can I have a drop down

I have three tables: categories, languages and categories_languages. Categories_languages is many to many table which links together categories and languages. I would like to update a foregin key value in table languages but it throws me error #1451 - Cannot delete or update a parent row: a foreign key constraint fails! CREATE TABLE IF NOT EXISTS `categories` ( `id` int(11) unsigned NOT NULL auto_increment, `name` varchar(20) NOT NULL, `modified` int(10) unsigned NOT NULL, PRIMARY KEY (`id`), ) ENGINE=InnoDB DEFAULT CHARSET=utf8; CREATE TABLE IF NOT EXISTS `languages` ( `id` char(2) NOT NULL,