primary-key

Let's say I have Person class Person{ @Id Integer id; @OneToOne @JoinColumn(name = "person_id") Job myJob; } and Job class Job{ @Id Integer id; Integer person_id; @OneToOne @PrimaryKeyJoinColumn(name = "person_id") Person currentWorker; } I'm not able to map the Person and Job to other Entity, when fetching. What mistake am I doing ? Guaido79 Your code should be: @Entity public class Person implements Serializable { @Id Integer id; @OneToOne @JoinColumn(name = "id") Job myJob; } @Entity public class Job implements Serializable { @Id Integer id; @OneToOne(mappedBy = "myJob") Person

I am trying to read up on best practices on DynamoDB. I saw that DynamoDB has two PK types: Hash Key Hash and Range Key From what I read, it appears the latter is like the former but supports sorting and indexing of a finite set of columns. So my question is why ever use only a hash key without a range key? Is it a viable choice only when the table is not searched? It'd also be great to have some general guidelines on when to use what key type. I've read several guides (including Amazon's own documentation on DynamoDB) but none of them appear to directly address this question. Thanks The

Since Oracle 12c we can use IDENTITY fields. Is there a way to retrieve the last inserted identity (i.e. select @@identity or select LAST_INSERTED_ID() and so on)? Well. Oracle uses sequences and default values for IDENTITY functionality in 12c. Therefore you need to know about sequences for your question. First create a test identity table. CREATE TABLE IDENTITY_TEST_TABLE ( ID NUMBER GENERATED ALWAYS AS IDENTITY , NAME VARCHAR2(30 BYTE) ); First, lets find your sequence name that is created with this identity column. This sequence name is a default value in your table. Select TABLE_NAME,

Is it possible to auto-increment a non-Primary Key? Table "book_comments" book_id medium_int timestamp medium_int user_id medium_int vote_up small_int vote_down small_int comment text comment_id medium_int Primary key -> (book_id, timestamp, user_id) There will be no other indexes on this table. However, I would like to make the comment_id column autoincrement so that I can easily create another table: Table "book_comments_votes" comment_id (medium_int) user_id (medium_int) Primary key -> (comment_id, user_id) Users would be able to vote only once per book comment. This table enforces this

I'm, generating a SQL query like this in PHP: $sql = sprintf("UPDATE %s SET %s = %s WHERE %s = %s", ...); Since almost every part of this query is dynamic I need a way to determine the table's primary key dynamically, so that I'd have a query like this: $sql = sprintf("UPDATE %s SET %s=%s WHERE PRIMARY_KEY = %s", ...); Is there a MySQL keyword for a table's primary key, or a way to get it? I've used the information_schema DB before to find information like this, but it'd be nice if I didn't have to resort to that. SHOW INDEX FROM <tablename> You want the row where Key_name = PRIMARY http://dev

I have a little witty problem. Say, I inserted a row with some data in a table where a primary key is present. How would one "SELECT" the primary key of the row one just inserted? I should have been more specific and mentioned that I'm currently using SQLite. For MS SQL Server: SCOPE_IDENTITY() will return you the last generated identity value within your current scope: SELECT SCOPE_IDENTITY() AS NewID For SQL Server 2005 and up, and regardless of what type your primary key is, you could always use the OUTPUT clause to return the values inserted: INSERT INTO dbo.YourTable(col1, col2, ....,

I'm trying to learn how to use keys and to break the habit of necessarily having SERIAL type IDs for all rows in all my tables. At the same time, I'm also doing many-to-many relationships, and so requiring unique values on either column of the tables that coordinate the relationships would hamper that. How can I define a primary key on a table such that any given value can be repeated in any column, so long as the combination of values across all columns is never repeated exactly? Adriaan Stander Quoted from the CREATE TABLE Syntax page: A PRIMARY KEY can be a multiple-column index. However,