CREATE TABLE. Use the LIKE clause instead of a full table definition to create a table with the same definition as another table, including columns, indexes, and table options. Foreign key definitions, as well as any DATA DIRECTORY or INDEX DIRECTORY table options specified on the original table, will not be created. CREATE TABLE. 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. He said, he knows the method where he can create the table and then apply the primary key with specific name.
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.
Basic Table Creation
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).
Using Identity and Primary Key Constraints
Sql Generate Create Table Script With Indexes And Primary Keys
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 IDENTITYcan 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).
Mysql Create Table Primary Key
With this new knowledge at our fingertips, we can rewrite our previous CREATE TABLE statement by adding our two new constraints.
T Sql Primary Key Create
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.