16.12.2020

Generate Primary Key Without Table

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Apr 22, 2010 It is interesting how sometimes the documentation of simple concepts is not available online. I had received email from one of the reader where he has asked how to create Primary key with a specific name when creating the table itself. Each table can only have one primary key. Access can automatically create a primary key field for you when you create a table, or you can specify the fields that you want to use as the primary key. This article explains how and why to use primary keys. To set a table’s primary key, open the table in Design view. A primary key is a column of a combination of columns in a table that uniquely identifies a row in the table. The following are rules that make a column a primary key: A primary key column cannot contain a NULL value or an empty string. A primary key value must be unique within the entire table. Creating a new table with a primary key requires CREATE TABLE permission in the database and ALTER permission on the schema in which the table is being created. Creating a primary key in an existing table requires ALTER permission on the table. Using SQL Server Management Studio To create a primary key. Jun 10, 2016  I think that the primary key absence would only affect some features like caching or whatever. Long term I'd guess if there is no primary key, or if the key contains multiple fields, you can just have the system generate its own such thing in memory composed of the combination of all the fields, maybe produce a unique hash code from them.

Jun 10, 2016 I think that the primary key absence would only affect some features like caching or whatever. Long term I'd guess if there is no primary key, or if the key contains multiple fields, you can just have the system generate its own such thing in memory composed of the combination of all the fields, maybe produce a unique hash code from them.

SQL PRIMARY KEY Constraint

The PRIMARY KEY constraint uniquely identifies each record in a table.

Primary keys must contain UNIQUE values, and cannot contain NULL values.

A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).

SQL PRIMARY KEY on CREATE TABLE

The following SQL creates a PRIMARY KEY on the 'ID' column when the 'Persons' table is created:

MySQL:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (ID)
);

SQL Server / Oracle / MS Access:

CREATE TABLE Persons (
ID int NOT NULL PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);

To allow naming of a PRIMARY KEY constraint, and for defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax:

MySQL / SQL Server / Oracle / MS Access:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
CONSTRAINT PK_Person PRIMARY KEY (ID,LastName)
);

Note: In the example above there is only ONE PRIMARY KEY (PK_Person). However, the VALUE of the primary key is made up of TWO COLUMNS (ID + LastName).

SQL PRIMARY KEY on ALTER TABLE

To create a PRIMARY KEY constraint on the 'ID' column when the table is already created, use the following SQL:

Generate Primary Key Without Table Of Life

MySQL / SQL Server / Oracle / MS Access:

To allow naming of a PRIMARY KEY constraint, and for defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax:

MySQL / SQL Server / Oracle / MS Access:

ALTER TABLE Persons
ADD CONSTRAINT PK_Person PRIMARY KEY (ID,LastName);

Note: If you use the ALTER TABLE statement to add a primary key, the primary key column(s) must already have been declared to not contain NULL values (when the table was first created).

DROP a PRIMARY KEY Constraint

To drop a PRIMARY KEY constraint, use the following SQL:

MySQL:

Generate Primary Key Without Tables

SQL Server / Oracle / MS Access:Windows 7 ultimate licence key generator.

Foreign Key