The Microsoft JDBC Driver for SQL Server supports the optional JDBC 3.0 APIs to retrieve automatically generated row identifiers. The main value of this feature is to provide a way to make IDENTITY values available to an application that is updating a database table without a requiring a query and a second round-trip to the server.
Learn how to define an auto increment primary key in SQL Server. This data tutorial will explain basic table creation and information around using identity a.
Because SQL Server doesn't support pseudo columns for identifiers, updates that have to use the auto-generated key feature must operate against a table that contains an IDENTITY column. SQL Server allows only a single IDENTITY column per table. The result set that is returned by getGeneratedKeys method of the SQLServerStatement class will have only one column, with the returned column name of GENERATED_KEYS. If generated keys are requested on a table that has no IDENTITY column, the JDBC driver will return a null result set.
As an example, create the following table in the sample database:
In the following example, an open connection to the sample database is passed in to the function, an SQL statement is constructed that will add data to the table, and then the statement is run and the IDENTITY column value is displayed.
Oct 20, 2017 Generating OpenVPN keys using Easy RSA It is possible to generate your certificates on the router itself if you don't have access to a Linux machine, or if you don't have a Windows client installed with Easy-RSA. Easy-RSA is a simple to use environment that is bundled with OpenVPN, and has been included in Asuswrt-Merlin. You now have all of the files necessary to configure an OpenVPN server. Step 6: Generate client credentials. You should generate a unique set of credentials for each and every client that will connect to your VPN. You can repeat this step for any client that you need to create credentials for. All clients in your setup should have a unique name. This is a small RSA key management package, based on the openssl command line tool, that can be found in the easy-rsa subdirectory of the OpenVPN distribution. 
Generating OpenVPN keys using Easy RSA. It is possible to generate your certificates on the router itself if you don't have access to a Linux machine, or if you don't have a Windows client installed with Easy-RSA. Easy-RSA is a simple to use environment that is bundled with OpenVPN, and has been included in.
See also
We can create Auto increment columns in oracle by using IDENTITY columns in Oracle 12c. And in Oracle Database does not have any exisiting feature to auto increment column values in table schema until Oracle 12c (mid 2014).
Auto increment columns widely used for auto-generating values for primary keys in Database tables.Most of the databases like SQL server etc have existing features to create auto increment columns.
In Oracle 12c they introduced IDENTITY columns which allows users to create auto increment columns.
In previous versions of Oracle this functionality developed using the combination of Sequences and Triggers.
In this tutorial I am going to explain these two ways to implement auto increment coulmns in Oracle database tables with examples,pros and cons of each method.
Table of Contents
Create Auto increment column in oracle By using IDENTITY Column example
Create an IDENTITY column by using following syntax
Now we can insert rows into the table
We have three options to create IDENTITY Column
- ALWAYS
- BY DEFAULT
- BY DEFAULT ON NULL
ALWAYS AS IDENTITY Example
We are using ALWAYS to force the use of IDENTITY. If we try to insert value into the IDENTITY column it will throw error saying cannot insert into a generated always identity column.
BY DEFAULT AS IDENTITY Example
Create IDENTITY column with BY DEFAULT option to insert values into IDENTITY column by referencing it in insert statement.
If you are specifying identity column in insert statment then it will insert whatever value we given if not then it will insert automatically incremented value into the IDENTITY column.
But we cannot insert NULL value it will throw error
BY DEFAULT ON NULL AS IDENTITY Example
Use BY DEFAULT ON NULL option to create identity column to use auto incremented value if you specily NULL in identity column in insert statement.
Additionally we can change the initial value of identity column and interval between the auto generated values by using following options. The default initial value and interval values for auto increment identity columns equals to 1.
- START WITH initial_value
- INCREMENT BY interval_value
In first table IDENTITY_STARTWITH the identity column starts with the value 10. and incremented by 1. Where as in second table IDENTITY_STARTWITH_INCR auto incemented column starts with 10 and incremented by 10.
When you create an identity column, Oracle generates 20 auto increment values before hand for performence reasons and Oracle recommends to include CACHE clause greater than the default of 20 to improve the performance.
Create auto increment column in oracle By using Sequences and Triggers Example
In earlier versions of Oracle we used to create auto increment columns using Sequences and Triggers.
Create a table and add primary key to that table
And then add primary key constraint
Sql Primary Key Create
Now we will create a sequence to generate unique auto incremented values.
A sequence is a data object that can be used by multiple users to generate auto increment values(no duplicate values will be generated).
We created sequence and but we are not using it. We will add a TRIGGER on table insert event.
Here we are creating a trigger named auto_increment_tb_insert which will be fired on each insertion on table auto_increment_tb.
We are getting next auto incremented value from created sequence by selecting auto_increment_tb_seq.nextval and inserting it into :new row of table ID column.
Best way to create auto increment column in oracle
Which is best way to insert auto incremented values into table? IDENTITY column or by using sequences and triggers?
Accroding oracle by using IDENTITY column in Oracle 12c is best way to create auto increment column than the older way of using Sequence and Triggers.
Sql Server Create Primary Key
Limitations of IDENTITY Coulmn
Sql Server Auto Generated Primary Key 2017
- We can add only one IDENTITY column per table.
- We can add identity_clause only on Numeric datatype columns not on User-defined data types.
- We cannot add DEFAULT clause in column defincation if we use identity_clause.
- We can create one table from another by adding a AS SELECT statement at the end of the CREATE TABLE for example “create table new_emp AS SELECT * from emp”; New table wont inherit IDENTITY property on column.
- When you add an identity_clause, then NOT NULL constraint and NOT DEFERRABLE constraint are added by default (implicitly specified). If you add an inline constraint that conflicts with NOT NULL and NOT DEFERRABLE, then an error will occur.