primary-key

I have a table user_interactions with 4 columns: user_1 user_2 type timestamp The primary key is (user_1,user_2,type) and I want to change to (user_2,user_1,type) So what I did was : drop primary key ... add primary key (user_2,user_1,type)... and voila... The problem is that database is live on a server. So before I could update the primary key, many duplicates already crept in, and they are continuously creeping in. What to do? What I want to do now is to remove duplicates and keep the ones with the latest timestamp (which is a column in the table). And then somehow update the primary key

I've read that compound primary keys will confuse the hell out of typical ORM code generators . Which ORMs work best with compound PKs and which to avoid? (I've a particular interest in .NET) I'm using NHibernate successfully with compound keys. <class name="UserProfileField" table="UserProfileFields"> <composite-id> <key-many-to-one name="Parent" column="UserId" lazy="false"/> <key-property name="FieldName"/> </composite-id> ... 来源： https://stackoverflow.com/questions/218100/orm-support-for-compound-primary-keys

I have a table which holds a list of IDs, and various other columns such as IDName. The Primary Key of the table is the ID itself, however it does not auto_increment. So, I want to be able to generate / calculate the next primary key, however there is a twist: The primary key should be in a specific format, i.e. the 8 digit ID is made up of three parts: <the level><a code><a sequence #> , e.g. <2><777><0123> = 27770123 So, when I am creating a new ID for the table, I want the next sequence number for a specific level and code. E.g. following the example above I might want to know the next

I'm trying to set up a Sybase query that will give me the following output: Table KeyType KeyNumber Column table1 PK 1 table1_id table1 FK 2 table2_id table1 FK 3 table3_id table1 FK 4 table4_id table1 Unique 5 table1_abc table1 Unique 5 table1_def In other words, I need the PK for each table, and every foreign key it has, as well as every unique key (not where a key has more than one element, such as the unique key above, this is identified by having the same KeyNumber). I'm guessing I need to use sysobject, syscolumns, syskeys and sysconstraints but I can't seem to figure out how they

I have two already-existing tables which look (in part) roughly like this: CREATE TABLE parent ( old_pk CHAR(8) NOT NULL PRIMARY KEY ) ENGINE=InnoDB; CREATE TABLE child ( parent_key CHAR(8), FOREIGN KEY (parent_key) REFERENCES parent(old_pk) ON UPDATE CASCADE ON DELETE CASCADE ) ENGINE=InnoDB; I want to add a new auto-incrementing integer id column to parent and use it as the primary key instead, while still keeping old_pk as a unique key and allowing other tables like child to reference it in foreign key contraints. Unfortunately, simply saying ALTER TABLE parent DROP PRIMARY KEY doesn't work

Paraphrasing from this MSDN documentation ... An INSERT statement is generated by the Entity Framework and executed on the data source when SaveChanges is called on the ObjectContext. If the INSERT operation succeeds, server-generated values are written back to the ObjectStateEntry. When AcceptChanges is called automatically at the end of the SaveChanges execution, a permanent EntityKey is computed by using the new server-generated values. This does not seem to be occurring in my code. When I call ObjectContext.SaveChanges() , an UpdateException is thrown with InnerException.Message value: