APPLIES TO: SQL Server 2016 and later Azure SQL Database Azure Synapse Analytics (SQL DW) Parallel Data Warehouse
You can define a primary key in SQL Server by using SQL Server Management Studio or Transact-SQL. Creating a primary key automatically creates a corresponding unique clustered index, or a nonclustered index if specified as such.
How to get primary key value (auto-generated keys) from inserted queries using JDBC? Description: When we are inserting a record into the database table and the primary key is an auto-increment or auto-generated key, then the insert query will generate it dynamically. Dec 05, 2011 In Oracle, you can create an auto increment field using âsequenceâ database object that can be assigned as primary keys. Using Oracle âsequenceâ object, you can generate new values for a column. An Oracle sequence is an object like a table or a stored procedure. Examples with walkthrough explanations are provided. Create a sequence. The primary keys typically are numeric because Oracle typically processes numbers faster than any other data types. It is considered a best practice have a primary key in every table though it is not mandatory in Oracle. To create a primary key in a table, you use the PRIMARY KEY constraint. Oracle PRIMARY KEY constraint examples.
Before You BeginLimitations and Restrictions
SecurityPermissions
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 StudioTo create a primary key
Caution
If you want to redefine the primary key, any relationships to the existing primary key must be deleted before the new primary key can be created. A message will warn you that existing relationships will be automatically deleted as part of this process.
A primary key column is identified by a primary key symbol in its row selector.
If a primary key consists of more than one column, duplicate values are allowed in one column, but each combination of values from all the columns in the primary key must be unique.
If you define a compound key, the order of columns in the primary key matches the order of columns as shown in the table. However, you can change the order of columns after the primary key is created. For more information, see Modify Primary Keys.
Using Transact-SQLTo create a primary key in an existing table
The following example creates a primary key on the column
TransactionID in the AdventureWorks database.
To create a primary key in a new table
The following example creates a table and defines a primary key on the column
TransactionID in the AdventureWorks database.
To create a primary key with clustered index in a new table
The following example creates a table and defines a primary key on the column
CustomerID and a clustered index on TransactionID in the AdventureWorks database.
See Also
This Oracle tutorial explains how to create, drop, disable, and enable a primary key in Oracle with syntax and examples.
What is a primary key in Oracle?
In Oracle, a primary key is a single field or combination of fields that uniquely defines a record. None of the fields that are part of the primary key can contain a null value. A table can have only one primary key.
Note
Create Primary Key - Using CREATE TABLE statement
You can create a primary key in Oracle with the CREATE TABLE statement.
Syntax
The syntax to create a primary key using the CREATE TABLE statement in Oracle/PLSQL is:
Example
Let's look at an example of how to create a primary key using the CREATE TABLE statement in Oracle:
In this example, we've created a primary key on the supplier table called supplier_pk. It consists of only one field - the supplier_id field.
We could also create a primary key with more than one field as in the example below:
Create Primary Key - Using ALTER TABLE statement
You can create a primary key in Oracle with the ALTER TABLE statement.
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Syntax
The syntax to create a primary key using the ALTER TABLE statement in Oracle/PLSQL is:
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Let's look at an example of how to create a primary key using the ALTER TABLE statement in Oracle.
In this example, we've created a primary key on the existing supplier table called supplier_pk. It consists of the field called supplier_id.
We could also create a primary key with more than one field as in the example below:
Drop Primary Key
You can drop a primary key in Oracle using the ALTER TABLE statement.
Oracle Primary Key TableSyntax
The syntax to drop a primary key using the ALTER TABLE statement in Oracle/PLSQL is:
Example
Let's look at an example of how to drop a primary key using the ALTER TABLE statement in Oracle.
In this example, we're dropping a primary key on the supplier table called supplier_pk.
Disable Primary Key
You can disable a primary key in Oracle using the ALTER TABLE statement.
Syntax
The syntax to disable a primary key using the ALTER TABLE statement in Oracle/PLSQL is:
Example
Let's look at an example of how to disable a primary using the ALTER TABLE statement in Oracle.
In this example, we're disabling a primary key on the supplier table called supplier_pk.
Enable Primary Key
You can enable a primary key in Oracle using the ALTER TABLE statement.
Syntax
The syntax to enable a primary key using the ALTER TABLE statement in Oracle/PLSQL is:
Example
Let's look at an example of how to enable a primary key using the ALTER TABLE statement in Oracle.
In this example, we're enabling a primary key on the supplier table called supplier_pk.
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