Question

请查看以下代码

package normal;

//This class if s for checking the database. If the database doesn't exists, this class will create one

import java.sql.*;

public class DatabaseCheck
{
    private Connection con;

    public DatabaseCheck()
    {
        createConnection();
        try
        {
            Statement st = con.createStatement();
            st.executeQuery("select * from PhoneData");
        }
        catch(Exception e)
        {
            System.out.println(e.getLocalizedMessage());

            if(e.getLocalizedMessage().equals("Schema 'SA' does not exist"))
            {
                try
                {
                PreparedStatement ps = con.prepareStatement("create table PhoneData(ids int identity constraint pkId primary key,names varchar(20),mobileNumber1 varchar(20),mobileNumber2 varchar(20),landNumber1 varchar(20),landNumber2 varchar(20),address varchar(100),category varchar(20),nickName varchar(20),email varchar(20),middleName varchar(20),lastName varchar(20),city varchar(20),country varchar(20))");
                ps.execute();

                PreparedStatement ps2 = con.prepareStatement("create table Emails(accountType varchar(10) constraint pk_user primary key,userName varchar(50) ,passwords varchar(50))");
                ps2.execute();

                }
                catch(Exception e2)
                {
                    e2.printStackTrace();
                }
            }
        }
        finally
        {
            closeConnection();
        }
    }

     public void createConnection()
    {
        try
        {
            Class.forName("org.apache.derby.jdbc.EmbeddedDriver");

            con = DriverManager.getConnection("jdbc:derby:PhoneBook;create=true","sa","sasasa");
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }

      public void closeConnection()
    {
        try
        {
            con.close();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
}

此类能够以编程方式在嵌入式apache derby数据库中创建表。但是，它会出现以下错误

java.sql.SQLSyntaxErrorException: Syntax error: Encountered "identity" at line 1, column 32.
    at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(Unknown Source)
    at org.apache.derby.impl.jdbc.Util.generateCsSQLException(Unknown Source)
    at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown Source)
    at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown Source)
    at org.apache.derby.impl.jdbc.ConnectionChild.handleException(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedPreparedStatement.<init>(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedPreparedStatement20.<init>(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedPreparedStatement30.<init>(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedPreparedStatement40.<init>(Unknown Source)
    at org.apache.derby.jdbc.Driver40.newEmbedPreparedStatement(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedConnection.prepareStatement(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedConnection.prepareStatement(Unknown Source)
    at normal.DatabaseCheck.<init>(DatabaseCheck.java:27)
    at normal.MyPhoneBookApp.main(MyPhoneBookApp.java:25)
Caused by: java.sql.SQLException: Syntax error: Encountered "identity" at line 1, column 32.
    at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
    at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(Unknown Source)
    ... 15 more
Caused by: ERROR 42X01: Syntax error: Encountered "identity" at line 1, column 32.
    at org.apache.derby.iapi.error.StandardException.newException(Unknown Source)
    at org.apache.derby.impl.sql.compile.ParserImpl.parseStatement(Unknown Source)
    at org.apache.derby.impl.sql.GenericStatement.prepMinion(Unknown Source)
    at org.apache.derby.impl.sql.GenericStatement.prepare(Unknown Source)
    at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.prepareInternalStatement(Unknown Source)
    ... 9 more

当我从表创建代码中删除“identity”关键字时，这工作正常。但是，必须自动生成ID。请帮忙！

Answer 1

Derby没有identity列类型（记录为in the manual）。您需要定义generated column。对于生成定义，Derby确实知道identity属性，但这不是数据类型。

因此ids的列定义应为

ids integer generated always as identity constraint pkId primary key

请注意，您也可以使用generated by default代替always。然后，只有在插入期间未指定该列的值时，才会生成值。 generated always将覆盖您提供的任何值。

Answer 2

Apache Derby documentation表示您可以将identity关键字替换为：

  NOT NULL GENERATED ALWAYS AS IDENTITY

Apache Derby：SQLSyntaxErrorException

2 个答案: