Sql Ystem-generated Primary Key That Is Usually Hidden From Users

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  1. By: Armando Prato Overview. Every table should have a primary key. A primary key is a unique, non-null value that identifies a row in the database. One of the most highly debated topics in the SQL Server world is deciding what type of data best makes a primary key.
  2. Values have no meaning to users and are usually hidden on forms, queries and reports. A surrogate key is often used in place of a composite primary key. Referential integrity states that every value of a foreign key must match a value of an existing primary key.

APPLIES TO: SQL Server 2016 and later Azure SQL Database Azure Synapse Analytics (SQL DW) Parallel Data Warehouse

What is Primary Key in SQL? A primary key is defined as the single column or a set of columns that uniquely identifies each row in the table. As soon as one primary key constraint is defined for the table, the database engine automatically creates a unique index for the primary key column.

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You can delete (drop) a primary key in SQL Server 2019 (15.x) by using SQL Server Management Studio or Transact-SQL. When the primary key is deleted, the corresponding index is deleted.

In This Topic

  • Before you begin:

  • To delete a primary key using:

Before You Begin

Security

Permissions

Requires ALTER permission on the table.

Using SQL Server Management Studio

To delete a primary key constraint using Object Explorer

  1. In Object Explorer, expand the table that contains the primary key and then expand Keys.

  2. Right-click the key and select Delete.

  3. In the Delete Object dialog box, verify the correct key is specified and click OK.

To delete a primary key constraint using Table Designer

  1. In Object Explorer, right-click the table with the primary key, and click Design.

  2. In the table grid, right-click the row with the primary key and choose Remove Primary Key to toggle the setting from on to off.

    Note

    To undo this action, close the table without saving the changes. Deleting a primary key cannot be undone without losing all other changes made to the table.

  3. On the File menu, click Savetable name.

Using Transact-SQL

To delete a primary key constraint

  1. In Object Explorer, connect to an instance of Database Engine.

  2. On the Standard bar, click New Query.

  3. Copy and paste the following example into the query window and click Execute. The example first identifies the name of the primary key constraint and then deletes the constraint.

For more information, see ALTER TABLE (Transact-SQL) and sys.key_constraints (Transact-SQL)

Sql System-generated Primary Key That Is Usually Hidden From Users Name

PRIMARY KEY

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

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A table can have only one primary key, which may consist of one single or of multiple fields.

SQL PRIMARY KEY on CREATE TABLE

Sql System-generated Primary Key That Is Usually Hidden From Users Guide

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:

Sql System-generated Primary Key That Is Usually Hidden From Users 2017

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

Sql System-generated Primary Key That Is Usually Hidden From Users List

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:

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:

SQL Server / Oracle / MS Access: