Question

我在过去的3个小时里到处都是，但仍然无法让它发挥作用。我需要能够连接1prefix和1suffix值，以形成一个由字符串和数字组成的id。

如何定义表格。

public class TestDatabase {
    private DBI dbi;
    private Handle handle;
    private CarDAO carDAO;

    @Before
    public void setUpDatabase() throws Exception {
        Environment environment = new Environment( "test-env", Jackson.newObjectMapper(), null, new MetricRegistry(), null );
        dbi = new DBIFactory().build( environment, getDataSourceFactory(), "cardb" );
        carDAO = dbi.onDemand(CarDAO.class);
        handle = dbi.open();
    }

    protected DataSourceFactory getDataSourceFactory()
    {
        DataSourceFactory dataSourceFactory = new DataSourceFactory();
        dataSourceFactory.setDriverClass( "com.mysql.jdbc.Driver" );
        dataSourceFactory.setUrl( "jdbc:mysql://127.0.0.1:3306/cardb" );
        dataSourceFactory.setUser( "root" );
        dataSourceFactory.setPassword( "root" );
        return dataSourceFactory;
    }

    @Test
    public void testCreatecar(){
        Car car = new Car("Test car","Test car teaser","http://localhost:8080/","#ff0000","car test description");
        Long carId = carDAO.createCar(car);
        assertNotNull(carId);
    }

    @Test
    public void testCreatecar2(){
        Car car = new Car("Test car","Test car teaser","http://localhost:8080/","#ff0000","car test description");
        Long carId = carDAO.createCar2(car);
        assertNotNull(carId);
    }
}

我需要能够生成

DISC0001 DISC0002 DISC0003

只有数字自动递增每次插入到DiscounName。我只想在主键前加上＆＃34; DISC＆＃34;作为折扣标识符。

我正在使用Derby。如果您可以帮助我或提供替代解决方案，我将非常感谢。

感谢。

Answer 1

生成的列应该完成这项工作。我没有要测试的Derby，但是后续工作可以在DB2中运行

create table t4 (prefix varchar(20) not null with default 'DISC',
                 suffix int generated always as identity (start with 1 increment by 1),
                 id generated always as (prefix || (substr2('000' || suffix, -4, 4))) )

Answer 2

另一种方法是使用SEQUENCE和NEXT VALUE FOR语法为主键生成新值，如下所示：http://db.apache.org/derby/docs/10.12/ref/rrefsqljnextvaluefor.html

例如，你可以这样做：

create sequence discount_ids start with 1;
insert into discounts (id, name) 
    values ( 'DISC' || cast( next value for discount_ids as char(20)),
             'bubble gum' );

在Derby DDL中如何将字符串和数字连接为标识

2 个答案: