Which Of The Following Sequence Settings Cannot Be Changed With The Alter Sequence Command?

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Oracle / PLSQL: Sequences (Autonumber)

This Oracle tutorial explains how to create and drop sequences in Oracle with syntax and examples.

Description

In Oracle, yous tin can create an autonumber field by using sequences. A sequence is an object in Oracle that is used to generate a number sequence. This can be useful when you need to create a unique number to act as a primary key.

Create Sequence

You may wish to create a sequence in Oracle to handle an autonumber field.

Syntax

The syntax to create a sequence in Oracle is:

CREATE SEQUENCE sequence_name   MINVALUE value   MAXVALUE value   Outset WITH value   INCREMENT By value   CACHE value;

sequence_name

The name of the sequence that you wish to create.

Case

Let's expect at an example of how to create a sequence in Oracle.

For instance:

CREATE SEQUENCE supplier_seq   MINVALUE 1   MAXVALUE 999999999999999999999999999   START WITH 1   INCREMENT Past 1   Cache twenty;

This would create a sequence object called supplier_seq. The kickoff sequence number that it would utilise is 1 and each subsequent number would increase past 1 (ie: 2,three,4,...}. It volition cache up to xx values for functioning.

If you omit the MAXVALUE choice, your sequence volition automatically default to:

MAXVALUE 999999999999999999999999999

So yous can simplify your CREATE SEQUENCE command as follows:

CREATE SEQUENCE supplier_seq   MINVALUE 1   Kickoff WITH 1   Increase BY i   Enshroud 20;

Now that you've created a sequence object to simulate an autonumber field, we'll cover how to retrieve a value from this sequence object. To call up the side by side value in the sequence social club, yous need to use nextval.

For example:

supplier_seq.NEXTVAL;

This would retrieve the adjacent value from supplier_seq. The nextval statement needs to be used in a SQL argument. For example:

INSERT INTO suppliers (supplier_id, supplier_name) VALUES (supplier_seq.NEXTVAL, 'Kraft Foods');

This insert statement would insert a new record into the suppliers tabular array. The supplier_id field would be assigned the adjacent number from the supplier_seq sequence. The supplier_name field would be set to Kraft Foods.

Drop Sequence

In one case yous take created your sequence in Oracle, you might observe that you demand to remove information technology from the database.

Syntax

The syntax to a driblet a sequence in Oracle is:

Drop SEQUENCE            sequence_name;

sequence_name

The name of the sequence that y'all wish to drop.

Example

Allow'southward look at an example of how to driblet a sequence in Oracle.

For example:

Drib SEQUENCE supplier_seq;

This example would drop the sequence called supplier_seq.

Frequently Asked Questions

One mutual question virtually sequences is:

Question: While creating a sequence, what does enshroud and nocache options mean? For example, you could create a sequence with a cache of 20 equally follows:

CREATE SEQUENCE supplier_seq   MINVALUE 1   Outset WITH ane   INCREMENT By 1   CACHE 20;

Or yous could create the same sequence with the nocache option:

CREATE SEQUENCE supplier_seq   MINVALUE ane   START WITH 1   Increment Past i   NOCACHE;

Respond: With respect to a sequence, the cache option specifies how many sequence values volition be stored in retention for faster access.

The downside of creating a sequence with a cache is that if a system failure occurs, all cached sequence values that have not be used, will exist "lost". This results in a "gap" in the assigned sequence values. When the system comes support, Oracle will cache new numbers from where it left off in the sequence, ignoring the then called "lost" sequence values.

TIP: To recover the lost sequence values, you tin can e'er execute an ALTER SEQUENCE command to reset the counter to the correct value.

Nocache ways that none of the sequence values are stored in retention. This option may sacrifice some performance, however, yous should not run into a gap in the assigned sequence values.

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Question: How do we set the LASTVALUE value in an Oracle Sequence?

Respond: You can change the LASTVALUE for an Oracle sequence, by executing an Change SEQUENCE control.

For example, if the final value used by the Oracle sequence was 100 and you would similar to reset the sequence to serve 225 as the next value. You would execute the following commands.

ALTER SEQUENCE seq_name Increase BY 124;  SELECT seq_name.nextval FROM dual;  ALTER SEQUENCE seq_name INCREMENT By one;

Now, the side by side value to be served by the sequence will be 225.

Source: https://www.techonthenet.com/oracle/sequences.php

Posted by: donaghyhtful1945.blogspot.com

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