Auto Generated Primary Key In Oracle

16.12.2020/ Comments off

As discussed in the documentation, a sequence in Oracle prevents duplicate values from being created simultaneously because multiple users are effectively forced to “take turns” before each sequential item is generated. For the purposes of creating a unique primary key for a new table, first we must CREATE the table we’ll be using. Aug 23, 2013 The above code should give us auto generated primary key value. The one thing to note here is method prepareStatement. We passed two arguments first the insert query string and second an array of column name. The column name should be the primary key column name of table where you inserting the record.

Unique Key

The AUTO_INCREMENT attribute can be used to generate a unique identity for new rows:

Which returns:

No value was specified for the AUTO_INCREMENT column, so MySQL assigned sequence numbers automatically. You can also explicitly assign 0 to the column to generate sequence numbers, unless the NO_AUTO_VALUE_ON_ZERO SQL mode is enabled. For example:

If the column is declared NOT NULL, it is also possible to assign NULL to the column to generate sequence numbers. For example:

When you insert any other value into an AUTO_INCREMENT column, the column is set to that value and the sequence is reset so that the next automatically generated value follows sequentially from the largest column value. For example:

Primary Key Generation Using Oracle's Sequence. Oracle provides the 'sequence' utility to automatically generate unique primary keys. To use this utility to auto-generate primary keys for a CMP entity bean, you must create a sequence table and use the ejbgen:automatic-key-generation tag to point to this table.
Hello, i want to define an entity bean with auto-generated primary key. The primary-key is a sequence declared in the db. In the 9AS documentation we found the way to declare auto-generated primary-keys. That means, we should declare the prim-key-class as java.long.Object and delete the prim-field in the ejb-jar. But this way doesn't work. What is the solution of this problem? Please help me.
May 28, 2017 In this video you will learn How to get primary key value (auto-generated keys) from inserted queries in JDBC using a demo project.

Updating an existing AUTO_INCREMENT column value in an InnoDB table does not reset the AUTO_INCREMENT sequence as it does for MyISAM and NDB tables.

You can retrieve the most recent automatically generated AUTO_INCREMENT value with the LAST_INSERT_ID() SQL function or the mysql_insert_id() C API function. These functions are connection-specific, so their return values are not affected by another connection which is also performing inserts.

Use the smallest integer data type for the AUTO_INCREMENT column that is large enough to hold the maximum sequence value you will need. When the column reaches the upper limit of the data type, the next attempt to generate a sequence number fails. Use the UNSIGNED attribute if possible to allow a greater range. For example, if you use TINYINT, the maximum permissible sequence number is 127. For TINYINT UNSIGNED, the maximum is 255. See Section 11.1.2, “Integer Types (Exact Value) - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT” for the ranges of all the integer types.

For a multiple-row insert, LAST_INSERT_ID() and mysql_insert_id() actually return the AUTO_INCREMENT key from the first of the inserted rows. This enables multiple-row inserts to be reproduced correctly on other servers in a replication setup.

To start with an AUTO_INCREMENT value other than 1, set that value with CREATE TABLE or ALTER TABLE, like this:

For information about AUTO_INCREMENT usage specific to InnoDB, see Section 14.9.1.4, “AUTO_INCREMENT Handling in InnoDB”.

For MyISAM tables, you can specify AUTO_INCREMENT on a secondary column in a multiple-column index. In this case, the generated value for the AUTO_INCREMENT column is calculated as MAX(auto_increment_column) + 1 WHERE prefix=given-prefix. This is useful when you want to put data into ordered groups.
Which returns:
In this case (when the AUTO_INCREMENT column is part of a multiple-column index), AUTO_INCREMENT values are reused if you delete the row with the biggest AUTO_INCREMENT value in any group. This happens even for MyISAM tables, for which AUTO_INCREMENT values normally are not reused.
If the AUTO_INCREMENT column is part of multiple indexes, MySQL generates sequence values using the index that begins with the AUTO_INCREMENT column, if there is one. For example, if the animals table contained indexes PRIMARY KEY (grp, id) and INDEX (id), MySQL would ignore the PRIMARY KEY for generating sequence values. As a result, the table would contain a single sequence, not a sequence per grp value.

More information about AUTO_INCREMENT is available here:

How to assign the AUTO_INCREMENT attribute to a column: Section 13.1.17, “CREATE TABLE Statement”, and Section 13.1.7, “ALTER TABLE Statement”.
How AUTO_INCREMENT behaves depending on the NO_AUTO_VALUE_ON_ZERO SQL mode: Section 5.1.10, “Server SQL Modes”.
How to use the LAST_INSERT_ID() function to find the row that contains the most recent AUTO_INCREMENT value: Section 12.15, “Information Functions”.
Setting the AUTO_INCREMENTVmware workstation 12 pro key generator. value to be used: Section 5.1.7, “Server System Variables”.
AUTO_INCREMENT and replication: Section 17.4.1.1, “Replication and AUTO_INCREMENT”.
Server-system variables related to AUTO_INCREMENT (auto_increment_increment and auto_increment_offset) that can be used for replication: Section 5.1.7, “Server System Variables”.

Primary Key Generation Using Oracle's Sequence

Oracle provides the 'sequence' utility to automatically generate unique primary keys. To use this utility to auto-generate primary keys for a CMP entity bean, you must create a sequence table and use the ejbgen:automatic-key-generation tag to point to this table.

In your Oracle database, you must create a sequence table that will create the primary keys, like is shown in the following example:

This creates a sequences of primary key, starting with 1, followed by 2, 3, and so forth. The sequence table in the example uses the default increment 1, but you can change this by specifying the increment keyword, such as increment by 3. When you do the latter, you must specify the exact same value in the cache-size attribute of the ejbgen:automatic-key-generation tag:

If you have specified automatic table creation in the CMP bean's project settings, the sequence table will be created automatically when the entity bean is deployed. For more information, see @ejbgen:jar-settings Annotation. For more information on the definition of a CMP entity bean, see below.

Primary Key Generation Using SQL Server's IDENTITY

In SQL Server (2000) you can use the 'IDENTITY' keyword to indicate that a primary-key needs to be auto-generated. The following example shows a common scenario where the first primary key value is 1, and the increment is 1:

In the CMP entity bean definition you need to specify SQLServer(2000) as the type of automatic key generator you are using. You can also provide a cache size:

Note. The SQLServer2000 option is the same as SQLServer, except that SQLServer uses @@IDENTITY column to get the generated key value and SQLServer2000 uses the SCOPE_IDENTITY() function instead.

Primary Key Generation Using a Named Sequence Table

A named sequence table is similar to the Oracle sequence functionality in that a dedicated table is used to generate primary keys. However, the named sequence table approach is vendor-neutral. To auto-generate primary keys this way, create a named sequence table using the two SQL statements shown in the example:

In the CMP entity bean definition you need to specify the named sequence table as the type of automatic key generator you are using. You can also provide a cache size:

Note. When you specify a cache-size for a named sequence table, a series of unique values are reserved for entity bean creation. When a new cache is necessary, a second series of unique values is reserved, under the assumption that the first series of unique values was entirely used. This guarantees that primary key values are always unique, although it leaves open the possibility that primary key values are not necessarily sequential. For instance, when the first series of values is 10..20, the second series of values is 21-30, even if not all values in the first series were actually used to create entity beans.

Defining the CMP Entity Bean

When defining a CMP entity bean that uses one of the primary key generators, you point to the name of the primary key generator table to obtain primary keys, using the ejbgen:automatic-key-generation tag. Also, you must define a primary key field of type Integer or Long, to set and get the auto-generated primary key. However, the ejbCreate method does not take a primary key value as an argument. Instead the EJB container adds the correct primary key to the entity bean record.

The following example shows what the entity bean might look like. Notice that the bean uses the named sequence option describe above, and that ejbCreate method does not take a primary key:

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