Auto-increment in Oracle without using a trigger

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What are the other ways of achieving auto-increment in oracle other than use of triggers?

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孤城傲影

2020-11-28 10:21

In addition to e.g. FerranB's answer:
It is probably worth to mention that, as opposed to how auto_incement works in MySQL:
sequences work database wide, so they can be used for multiple tables and the values are unique for the whole database
therefore: truncating a table does not reset the 'autoincrement' functionaltiy

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鱼传尺愫

2020-11-28 10:22

From 12c you can use an identity column, which makes explicit the link between table and auto-increment; there's no need for a trigger or a sequence. The syntax would be:

create table <table_name> ( <column_name> generated as identity );

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情歌与酒

2020-11-28 10:24

SELECT max (id) + 1 
FROM   table

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死守一世寂寞

2020-11-28 10:32

Create a sequence:

create sequence seq;

Then to add a value

insert into table (id, other1, other2)
values (seq.nextval, 'hello', 'world');

Note: Look for oracle docs for more options about sequences (start value, increment, ...)

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天涯浪人

2020-11-28 10:37

If you don't really want to use a "trigger-based" solution, you can achieve the auto-increment functionality with a programmatical approach, obtaining the value of the auto increment key with the getGeneratedKeys() method.

Here is a code snippet for your consideration:

Statement stmt = null;
ResultSet rs = null;

stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
                                java.sql.ResultSet.CONCUR_UPDATABLE);

stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTable");

stmt.executeUpdate("CREATE TABLE autoIncTable ("
                + "priKey INT NOT NULL AUTO_INCREMENT, "
                + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

stmt.executeUpdate("INSERT INTO autoIncTable  (dataField) "
                + "values ('data field value')",
                Statement.RETURN_GENERATED_KEYS);

int autoIncKeyFromApi = -1;

rs = stmt.getGeneratedKeys();

if (rs.next()) {
    autoIncKeyFromApi = rs.getInt(1);
}
else {
    // do stuff here        
}

rs.close();

source: http://forums.oracle.com/forums/thread.jspa?messageID=3368856

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粉色の甜心

2020-11-28 10:38

A trigger to obtain the next value from a sequence is the most common way to achieve an equivalent to AUTOINCREMENT:

create trigger mytable_trg
before insert on mytable
for each row
when (new.id is null)
begin
    select myseq.nextval into :new.id from dual;
end;

You don't need the trigger if you control the inserts - just use the sequence in the insert statement:

insert into mytable (id, data) values (myseq.nextval, 'x');

This could be hidden inside an API package, so that the caller doesn't need to reference the sequence:

mytable_pkg.insert_row (p_data => 'x');

But using the trigger is more "transparent".

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