SQL PRIMARY KEY Constraint
The PRIMARY KEY constraint uniquely identifies each record in a table.
Apr 05, 2020 This post explains how to implement table partitioning for an existing table in SQL Server. Let us create a table as below for our explanation. Create Table and Populate table data Create Table AuditData (ID int identity(1,1) Primary Key not null, AuditDate Datetime not null) Insert into AuditData Values(getdate - (365.5)),(getdate - (365.4)),(getdate. Using NEWID in a CREATE TABLE statement. Applies to: SQL Server. The following example creates the cust table with a uniqueidentifier data type, and uses NEWID to fill the table with a default value. In assigning the default value of NEWID, each new and existing row has a unique value for the CustomerID column.- Creating a table using NEWID for uniqueidentifier data type. By default, the primary key on a SQL Server table is also used as the clustering key - but that doesn't need to be that way! I've personally seen massive performance gains when breaking up the previous GUID-based Primary / Clustered Key into two separate key - the primary (logical) key on the GUID, and the clustering (ordering) key on a separate INT IDENTITY(1,1) column. Having read some articles about how using a GUID for a primary key is such a bad idea with regards to a clustered index, I'd like to see if anyone has any insights where it might be acceptable. (at least in v4 GUIDs which SQL Server generates). Can generate a key that is almost certainly unique. Mar 05, 2009 Relational theory says that every table MUST have a primary key. SQL Server does not have this requirement. However, many features – like replication – often have a requirement on a primary key so that they can guarantee which row to modify on a related database/server (like the subscriber in a replication environment). Detriments to GUIDs as a Primary Key: They are large 16 bytes meaning they will consume more space as indexes and foreign keys are added. They do not sort well as they are essentially random numbers. Index usage is very, very, very bad. A lot of leaf moving.
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).
![Primary Primary](/uploads/1/2/5/8/125872399/215487644.png)
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)
);
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
);
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)
);
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:
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ALTER TABLE Persons
ADD CONSTRAINT PK_Person PRIMARY KEY (ID,LastName);
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:
-->
Creates a unique value of type uniqueidentifier.
Syntax
Return Types
uniqueidentifier
Remarks
NEWID()
is compliant with RFC4122.Examples
A. Using the NEWID function with a variable
The following example uses
NEWID()
to assign a value to a variable declared as the uniqueidentifier data type. The value of the uniqueidentifier Shogun total war cd key generator. data type variable is printed before the value is tested.Here is the result set.
Note
The value returned by NEWID is different for each computer. This number is shown only for illustration.
B. Using NEWID in a CREATE TABLE statement
Applies to: SQL Server
The following example creates the
cust
table with a uniqueidentifier data type, and uses NEWID to fill the table with a default value. In assigning the default value of NEWID()
, each new and existing row has a unique value for the CustomerID
column.Sql Server Generate Guid Primary Key Tutorial
C. Using uniqueidentifier and variable assignment
The following example declares a local variable called
@myid
as a variable of uniqueidentifier data type. Then, the variable is assigned a value by using the SET
Wavepad sound editor key generator torrent. statement.See Also
Sql Server Generate Guid Primary Key 2017
NEWSEQUENTIALID (Transact-SQL)
ALTER TABLE (Transact-SQL)
CAST and CONVERT (Transact-SQL)
CREATE TABLE (Transact-SQL)
Data Types (Transact-SQL)
System Functions (Transact-SQL)
uniqueidentifier (Transact-SQL)
Sequence Numbers
ALTER TABLE (Transact-SQL)
CAST and CONVERT (Transact-SQL)
CREATE TABLE (Transact-SQL)
Data Types (Transact-SQL)
System Functions (Transact-SQL)
uniqueidentifier (Transact-SQL)
Sequence Numbers