primary-key - w3toppers.com

Multi-Column Primary Key in MySQL 5

Quoted from the CREATE TABLE Syntax page: A PRIMARY KEY can be a multiple-column index. However, you cannot create a multiple-column index using the PRIMARY KEY key attribute in a column specification. Doing so only marks that single column as primary. You must use a separate PRIMARY KEY(index_col_name, …) clause. Something like this can be … Read more

MySQL – Meaning of “PRIMARY KEY”, “UNIQUE KEY” and “KEY” when used together while creating a table

A key is just a normal index. A way over simplification is to think of it like a card catalog at a library. It points MySQL in the right direction. A unique key is also used for improved searching speed, but it has the constraint that there can be no duplicated items (there are no … Read more

How can I set two primary key fields for my models in Django?

Update Django 4.0 Django 4.0 documentation recommends using UniqueConstraint with the constraints option instead of unique_together. Use UniqueConstraint with the constraints option instead. UniqueConstraint provides more functionality than unique_together. unique_together may be deprecated in the future. class Hop(models.Model): migration = models.ForeignKey(‘Migration’) host = models.ForeignKey(User, related_name=”host_set”) class Meta: constraints = [ models.UniqueConstraint( fields=[‘migration’, ‘host’], name=”unique_migration_host_combination” ) … Read more

Reset PostgreSQL primary key to 1

The best way to reset a sequence to start back with number 1 is to execute the following: ALTER SEQUENCE <tablename>_<id>_seq RESTART WITH 1 So, for example for the users table it would be: ALTER SEQUENCE users_id_seq RESTART WITH 1

adding primary key to sql view

We can add a disabled primary key constraint to a view. That is, the constraint does not fire if an insert or update is run against the view. The database expects integrity to be maintained through constraints on the underlying tables. So the constraint exists solely for the purposes of documentation. SQL> create view emp_view … Read more

SQL – Inserting a row and returning primary key

For MS SQL Server: SCOPE_IDENTITY() will return you the last generated identity value within your current scope: SELECT SCOPE_IDENTITY() AS NewID

Composite PRIMARY KEY enforces NOT NULL constraints on involved columns

If you need to allow NULL values, use a UNIQUE constraint (or index) instead of a PRIMARY KEY (and add a surrogate PK column – I suggest a serial or IDENTITY column in Postgres 10 or later). Auto increment table column A UNIQUE constraint allows columns to be NULL: CREATE TABLE distributor ( distributor_id GENERATED … Read more

How to make a primary key start from 1000?

If your table has already been created with an auto-increment. so you can use ALTER TABLE tbl AUTO_INCREMENT = 1000; otherwise put the AUTO_INCREMENT = 1000; in your CREATE TABLE it goes before the final );

How to get primary key of table?

A better way is to use SHOW KEYS since you don’t always have access to information_schema. The following works: SHOW KEYS FROM table WHERE Key_name=”PRIMARY” Column_name will contain the name of the primary key.

Hibernate, alter identifier/primary key

Actually, according to the JPA specification it is forbidden to change a primary key: The application must not change the value of the primary key[8]. The behavior is undefined if this occurs.[9] (from EJB 3 persistence (JPA) specification, paragraph 2.1.4)