relational-database

I have a column with a uniqueidentifier that can potentially reference one of four different tables. I have seen this done in two ways, but both seem like bad practice. First, I've seen a single ObjectID column without explicitly declaring it as a foreign key to a specific table. Then you can just shove any uniqueidentifier you want in it. This means you could potentially insert IDs from tables that are not part of the 4 tables I wanted. Second, because the data can come from four different tables, I've also seen people make 4 different foreign keys. And in doing so, the system relies on ONE

I feel like I'm being stupid, but I can't find anywhere on the phpMyAdmin interface to add constraints to foreign keys e.g. CASCADE ON DELETE I've looked for similar questions on here and on the phpMyAdmin wiki but I can't find anything about it. I realise I could do this via the query interface, but I'd like to know how to do it through the graphical interface. First, you should have your storage engine as InnoDB. Then select a table and go to 'Structure' tab. Under the table you will see 'Relation view', click it. From there you could add constraints. CASCADE Whenever rows in the master

Suppose I have a table of objects structured in a hierarchy: A |--B |--C | +--D +--E They are stored in a "parent-child" table thus: parent child A B A C C D A E How do I query this to get the structure defined above? I think I need something that produces info like this: object full_path A NULL B A C A D A.C E A I cannot figure out how to do the objects nested more than one level deep. It feels like I might need to iterate over the table (no idea if this is possible in SQL), or otherwise use some kind of query I've never encountered before. Additional Info: A need not be the only orphan

What's the standard relational database idiom for setting permissions for items? Answers should be general; however, they should be able to be applied to example below. Anything flies: adding columns, adding another table—whatever as long as it works well. Application / Example Assume the Twitter database is extremely simple: we have one User table, which contains a login and user id; we have a Tweet table, which contains a tweet id, tweet text, and creator id; and we have a Follower table, which contains the id of the person being followed and the follower. Now, assume Twitter wants to enable

I am just learning how to implement the Nested Set Model but still have confusion with a certain aspect of it involving items that may be part of multiple categories. Given the example below that was pulled from HERE and mirrors many other examples I have come across... How do you avoid duplication in the DB when you add Apples since they are multi-colored (i.e. Red, Yellow, Green)? Lachezar Balev You do not avoid duplications and the apple (or a reference to the apple) will be placed twice in your tree otherwise it won't be a tree but rather a graph. Your question is equally applicable if you

I am trying to set up a normalised MySQL database containing the three following tables. The first table contains a list of items which can be described by various tags. The third table contains the various tags used to describe the items in the first table. The middle table relates the other two tables to each other. In each table's case, the id is an auto-incrementing primary key (and each is used as the foreign key in the middle table) +---------------+---------------------+---------------+ | Table 1 | Table 2 | Table 3 | +---------------+---------------------+---------------+ |id item |id

I'm developing a Microsoft Access 2013 based information system. One of the client's demands was to simplify the data entry process by using combo box with available values. For example, instead of entering agentID the client asked to let the user choose agent name from the combo box, the same logic with other similar fields. In brief: I need to avoid as much as possible the need to enter the values ID and let to user choose them from the combo box. Microsoft Access has a built-in lookup wizard that allows to user to bind the table field with specific field from another table, e.g. to link

A question: I have 2 tables: Product id INT name VARCHAR(64) something TEXT else INT entirely BOOL and Ingredient id INT name VARCHAR(64) description TEXT Now I also have a link table Products_Ingredients product_id INT ingredient_id INT for my many to many relation. Now both products and ingredients will have unique names. So I can use names as natural keys... however will that be a good idea? Say I have a product: Paint Thinner Supreme with ingredient: Butylonitrotetrocycline Will that be a good idea to use those names as composite key in the link table? As much as I understand idea behind