foreign-keys

I'm designing my database schema using MySQL Workbench, which is pretty cool because you can do diagrams and it converts them :P Anyways, I've decided to use InnoDB because of it's Foreign Key support. One thing I noticed though is that it allows you to set On Update and on Delete options for foreign keys. Can someone explain where "Restrict", "Cascade" and set null could be used in a simple example? For example, say I have a user table which includes a userID . And say I have a message table message which is a many-to-many which has 2 foreign keys (which reference the same primary key, userID

My current db design is in the screenshot. It seems flawed because there is no enforced relationship (pk/fk) between the t_criteria_director and the t_criteria_a b c d e f... tables. Is there a better way to design this one to many scenario to keep referential integrity? Your design doesn't "seem" anything because we can't read your mind. You have given some aspects of a design but not the business "scenario" it represents/implements/describes or how it does so. SQL NULL, UNIQUE, PKs & FKs are kinds of constraints. A constraint is a limitation on what database values can appear. An SQL FK says

I have a table Users with a field called org_id which is a foreign key to a table organisation , with primary key field organisation_id . Knowing the table name (users) and the field name ( users.org_id ), is there a query that can tell me the name and field that org_id references? I've found a Stackoverflow post similar to this where a query was provided to determine the referenced table name, but I also need to know the field name that is referenced: SELECT c.confrelid::regclass::text AS referenced_table ,c.conname AS fk_name ,pg_get_constraintdef(c.oid) AS fk_definition FROM pg_attribute a

The following are two partial tables in which I am trying to define a foreign key relationship. public class Form { [Key, Column("FormID")] public System.Guid FormGUID { get; set; } [Column("PatGUID")] public Nullable<System.Guid> PatientGUID { get; set; } } public class Patient { [Column("PatGUID")] public System.Guid PatientGUID { get; set; } [Key, Column("PatID")] public int PatientID { get; set; } } I've eliminated all but the relevant information, fields, navigations, etc. for this example; hopefully not too much. We have a table Form, with a FK of PatGUID to a Patient table with field

I am struggling with foreign keys in my DB, possibly it has something to do with inheritance? So here's the basic setup: -- table address CREATE TABLE address ( pk_address serial NOT NULL, fk_gadmid_0 integer NOT NULL, -- this table already exists, no problem here street character varying(100), zip character varying(10), city character varying(50), public boolean, CONSTRAINT address_primarykey PRIMARY KEY (pk_address), CONSTRAINT gadmid_0_primarykey FOREIGN KEY (fk_gadmid_0) REFERENCES adm0 (gadmid_0) MATCH SIMPLE ON UPDATE CASCADE ON DELETE NO ACTION ) WITH ( OIDS=FALSE ); ALTER TABLE address