All can be done in SQL Server Management Studio. The Script Table As option generates create code for primary and foreign keys and constraints. It doesn't create script for the indexes, so you have to do that in another step. Type, I suggest expanding all object type nodes in SSMS Object Explorer. 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).
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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.
A table can contain only one PRIMARY KEY constraint.
All columns defined within a PRIMARY KEY constraint must be defined as NOT NULL. If nullability is not specified, all columns participating in a PRIMARY KEY constraint have their nullability set to NOT NULL.
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.
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.
The following example creates a primary key on the column TransactionID
in the AdventureWorks database.
The following example creates a table and defines a primary key on the column TransactionID
in the AdventureWorks database.
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.
Similar to MySQL, PostgreSQL, Oracle, and many other relational databases, SQL Server is best utilized when assigning unique primary keys to most database tables.
The advantages to using numeric, auto incremented primary keys are numerous, but the most impactful benefits are faster speed when performing queries and data-independence when searching through thousands of records which might contain frequently altered data elsewhere in the table. With a consistent and unique numeric identifier, applications can take advantage of these faster and more reliable queries.
Once connected to your SQL Server, you’d normally start by CREATING
a new table that contains the the field you wish to use as your incremented primary key. For our example, we’ll stick with the tried and true id
field:
The problem here is, we have no way of controlling our id
field. When a new record is inserted, we not only must manually enter a value for id
, but we have to perform a query ahead of time to attempt to verify that id
value doesn’t already exist (a near-impossibility when dealing with many simultaneous connections).
The solution turns out to be using two constraint options provided by SQL Server.
The first is PRIMARY KEY
, which as the name suggests, forces the specified column to behave as a completely unique index for the table, allowing for rapid searching and queries.
While SQL Server only allows one PRIMARY KEY
constraint assigned to a single table, that PRIMARY KEY
can be defined for more than one column. In a multi-column scenario, individual columns can contain duplicate, non-unique values, but the PRIMARY KEY
constraint ensures that every combination of constrained values will in fact be unique relative to every other combination.
The second piece of the puzzle is the IDENTITY
constraint, which informs SQL Server to auto increment the numeric value within the specified column anytime a new record is INSERTED
. While IDENTITY
can accept two arguments of the numeric seed
where the values will begin from as well as the increment
, these values are typically not specified with the IDENTITY
constraint and instead are left as defaults (both default to 1
).
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With this new knowledge at our fingertips, we can rewrite our previous CREATE TABLE
statement by adding our two new constraints.
That’s all there is to it. Now the id
column of our books
table will be automatically incremented upon every INSERT
and the id
field is guaranteed to be a unique value as well.