Cratedb Generated Column Primary Key

Further Reading: The great primary-key debate or just Google meaningless primary keys or even peruse this SO question. FWIW - My 2 cents is to avoid multi-column primary keys and use a single generated id field (surrogate key) as the primary key and add additional (unique) constraints where necessary. CREATE TABLE will create a new, initially empty table. A generated column is not a virtual column. The computed value is stored in the table like a base column is. The automatic computation of the value is what makes it different. The default is the primary key if specified, otherwise the internal id column. PARTITIONED BY. ∟ Tables with Primary Key Column 'GENERATED. AS IDENTITY' This section describes how to create a table primary key column defined as 'GENERATED. AS IDENTITY'.  Similar to Microsoft SQL Server, Derby supports IDENTITY columns to help you creating. Insert from dynamic queries constraints ¶. In some cases SELECT statements produce invalid data. This opens a rare occasion for inconsistent outcomes. If the select statement produces data where a few rows contain invalid column names, or where you have rows which types are not compatible among themselves, some rows will be inserted while others will fail.

  1. Cratedb Generated Column Primary Key Data

This annotation specifies a primary key column that is used as a foreign key to join to another table.

It is used to join the primary table of an entity subclass in the JOINED mapping strategy to the primary table of its superclass; it is used within a SecondaryTable annotation to join a secondary table to a primary table; and it may be used in a OneToOne mapping in which the primary key of the referencing entity is used as a foreign key to the referenced entity.

If no PrimaryKeyJoinColumn annotation is specified for a subclass in the JOINED mapping strategy, the foreign key columns are assumed to have the same names as the primary key columns of the primary table of the superclass

Since:
Java Persistence 1.0
Optional Element Summary
StringcolumnDefinition
(Optional) The SQL fragment that is used when generating the DDL for the column.
Stringname
The name of the primary key column of the current table.
StringreferencedColumnName
(Optional) The name of the primary key column of the table being joined to.

name

The name of the primary key column of the current table.

Defaults to the same name as the primary key column of the primary table of the superclass (JOINED mapping strategy); the same name as the primary key column of the primary table (SecondaryTable mapping); or the same name as the primary key column for the table for the referencing entity (OneToOne mapping)

Cratedb Generated Column Primary Key Data

Default:
'

referencedColumnName

(Optional) The name of the primary key column of the table being joined to.

Defaults to the same name as the primary key column of the primary table of the superclass (JOINED mapping strategy); the same name as the primary key column of the primary table (SecondaryTable mapping); or the same name as the primary key column for the table for the referencing entity (OneToOne mapping)

Default:
'

columnDefinition

Column(Optional) The SQL fragment that is used when generating the DDL for the column. This should not be specified for a OneToOne primary key association.

Defaults to the generated SQL to create a column of the inferred type.

Default:
'
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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 @AutomaticKeyGeneration annotation to point to this table.

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

This creates a sequences of primary key values, 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 cacheSize attribute of the @AutomaticKeyGeneration annotation:

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 @JarSettings 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 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:

Key

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 @JarSettings Annotation. For more information on the definition of a CMP entity bean, see below.

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:

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 @JarSettings Annotation. For more information on the definition of a CMP entity bean, see the next section.

Note. When you specify a cacheSize value 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 use the the @AutomaticKeyGeneration annotation to point to the name of the primary key generator table to obtain primary keys. 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 described above, and that ejbCreate method does not take a primary key:

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