Apache Derby ID列应自动一一递增-但事实并非如此，为什么? [英] Apache Derby ID column should auto increment one by one - but it does not, why?

问题描述

我正在尝试创建一个Apache Derby-Table，并通过JDBC接口在其中插入数据.

I'm trying to create an Apache Derby-Table and to insert data in it by the JDBC-interface.

这是我的实现的简短摘录:

Here is a short excerpt of my implementation:

public class SQLDatabase {

    private Connection connection = null;
    public final static String HOME_DIRECTORY = System.getProperty("user.home");
    public final static String TABLE_NAME = "PORPHYRIE";

    public SQLDatabase() {

        setConnection();
        if (!(isTableExisting(TABLE_NAME))) {

            createTable();
        }

    }




    // OTHER

    public void createTable() {
        String statement = "CREATE TABLE PORPHYRIE("
                + "ID int NOT NULL GENERATED ALWAYS AS IDENTITY"
                + "(START WITH 1,INCREMENT BY 1)," + "ENTRYDATE DATE NOT NULL,"
                + "DRUGTYPE varchar(255) NOT NULL,"
                + "UPPERLIMIT DOUBLE NOT NULL," + "NORMOSANG BOOLEAN NOT NULL,"
                + "MENSTRUATION BOOLEAN NOT NULL,"
                + "DRUGAMOUNT_MG DOUBLE NOT NULL,"
                + "DRUGAMOUNT_ML DOUBLE NOT NULL,"
                + "AMPOULE_NUMBERS DOUBLE NOT NULL,"
                + "RECORDDATE DATE NOT NULL," + "PRIMARY KEY(ID)" + ")";
        updateStatement(statement);
    }

    public void dropTable() {
        String statement = "DROP TABLE PORPHYRIE";
        updateStatement(statement);
    }

    public void addData(EntryPoint entry) {
        DrugAmount drugAmount = entry.getDrugAmountObject();
        SimpleDateFormat form = new SimpleDateFormat("dd.MM.yyyy");
        String statement = "INSERT INTO PORPHYRIE (ENTRYDATE,DRUGTYPE,UPPERLIMIT,NORMOSANG,MENSTRUATION,DRUGAMOUNT_MG,DRUGAMOUNT_ML,AMPOULE_NUMBERS,RECORDDATE)"
                + " values('"
                + form.format(entry.getEntryDate().getTime())
                + "','"
                + entry.DRUG_TYPE_DOLANTIN
                + "',"
                + entry.DRUG_UPPER_LIMIT
                + ","
                + entry.getNormoSang()
                + ","
                + entry.getMenstruation()
                + ","
                + drugAmount.getAmpoulesInMG()
                + ","
                + drugAmount.getAmpoulesInML()
                + ","
                + drugAmount.getNumberOfAmpoules() + ",CURRENT_DATE)";
        System.out.println("Add data!");
        updateStatement(statement);
    }


   private void setConnection() {
        try {
            Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
            connection = DriverManager.getConnection("jdbc:derby:"
                    + HOME_DIRECTORY + "\\MyDB;create=true");
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }
    }
    private void updateStatement(String statementString) {
        try {
            PreparedStatement preparedStatement = getConnection()
                    .prepareStatement(statementString);
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

这就是我得到的:

这里的ID列有什么问题?

What is here the problem with the ID column?

第一次创建SQL-Database对象时，应创建表，该表工作正常. 然后，您应该可以通过addData()方法插入一些数据，这看起来也不错. 但是，如果您创建一个新的SQL数据库对象并在其中使用addData-method()，则它将添加数据(上图中的第5行)，但不会正确自动递增.这是怎么了

The first time when a SQL-Database object is created, is should create the table, which works fine. Then you should able to insert some data by the addData()-method, which also looks fine. But if you create an new SQL-Database Object and use the addData-method() within, then it adds the data (row five in the picture above) but do not auto-increment correctly. What is wrong here?

推荐答案

生成的序列号中的空白是Derby的正确且有据可查的行为.

Gaps in the generated sequence numbers are a correct and documented behavior of Derby.

例如，参见 https://db.apache.org /derby/docs/10.9/ref/rrefproperpreallocator.html

并且: https://issues.apache.org/jira/browse/DERBY- 5151

这篇关于Apache Derby ID列应自动一一递增-但事实并非如此，为什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！