Question

我必须在数据库中创建3个表。因此，我定义表的列和行并执行SQLite命令。但是，当我尝试向表中添加一些值时，它会给我一个运行时错误。与此相反，当我只创建一个特定的表并在运行时向其添加值时，事情似乎正常。下面是数据库创建类：

public class StockDatabase extends SQLiteOpenHelper{


public static final String DATABASE_NAME="Accountancy";

public static final int DATABASE_VERSION=7;

public static String createPurchaseTable= "CREATE TABLE stock (_id INTEGER PRIMARY KEY AUTOINCREMENT, item_name TEXT NOT NULL, quant INTEGER NOT NULL, Prate REAl NOT NULL, Srate REAL NOT NULL);";
public static String createSaleTable="CREATE TABLE i/o_register (_id INTEGER PRIMARY KEY AUTOINCREMENT, item_code INTEGER NOT NULL, quantity INTEGER NOT NULL, rate REAL NOT NULL);";
public static String createRegister="CREATE TABLE s/p_register (PartyName TEXT NOT NULL, range TEXT NOT NULL, date TEXT NOT NULL, type INTEGER NOT NULL);";


public StockDatabase(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    // TODO Auto-generated constructor stub

}

@Override
public void onCreate(SQLiteDatabase db) {
    // TODO Auto-generated method stub
    db.execSQL(createPurchaseTable);
    db.execSQL(createSaleTable);
    db.execSQL(createRegister);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // TODO Auto-generated method stub
    db.execSQL("DROP TABLE IF EXISTS stock");
    db.execSQL("DROP TABLE IF EXISTS i/o_register");
    db.execSQL("DROP TABLE IF EXISTS s/p_register");
    onCreate(db);
    }

   }

CASE：当只在数据库中创建'stock'表时。当我尝试在'stock'表中添加一些值时，一切都很完美。

CASE：在数据库中创建3个表时我尝试在stock表中添加值，但它给了我一个nullPointerException。

Answer 1

尝试在更改DATABASE_VERSION（即数据库中当前为7）后创建新表。

修改

现在尝试以这种方式创建一个表：

public class DatabaseManager { // the Activity or Application that is creating an object from this class. Context context; // a reference to the database used by this application/object private SQLiteDatabase db; // These constants are specific to the database. They should be // changed to suit your needs. private final String DB_NAME = "database_name_2"; private final int DB_VERSION = 8; // These constants are specific to the database table. They should be // changed to suit your needs. private final String TABLE_NAME = "database_table"; private final String TABLE_ROW_ID = "id"; private final String TABLE_ROW_ONE = "table_row_one"; private final String TABLE_ROW_TWO = "table_row_two"; private final String TABLE_ROW_THREE = "table_row_three"; public DatabaseManager(Context context) { this.context = context; // create or open the database CustomSQLiteOpenHelper helper = new CustomSQLiteOpenHelper(context); this.db = helper.getWritableDatabase(); } /********************************************************************** * ADDING A ROW TO THE DATABASE TABLE * * This is an example of how to add a row to a database table using this * class. You should edit this method to suit your needs. * * the key is automatically assigned by the database * * @param rowStringOne * the value for the row's first column * @param rowStringTwo * the value for the row's second column */ public void addRow(String rowStringOne, String rowStringTwo, String qty) { // this is a key value pair holder used by android's SQLite functions ContentValues values = new ContentValues(); values.put(TABLE_ROW_ONE, rowStringOne); values.put(TABLE_ROW_TWO, rowStringTwo); values.put(TABLE_ROW_THREE, qty); // ask the database object to insert the new data try { db.insert(TABLE_NAME, null, values); } catch (Exception e) { Log.e("DB ERROR", e.toString()); e.printStackTrace(); } } /********************************************************************** * DELETING A ROW FROM THE DATABASE TABLE * * This is an example of how to delete a row from a database table using * this class. In most cases, this method probably does not need to be * rewritten. * * @param rowID * the SQLite database identifier for the row to delete. */ public void deleteRow(long rowID) { // ask the database manager to delete the row of given id try { db.delete(TABLE_NAME, TABLE_ROW_ID + "=" + rowID, null); } catch (Exception e) { Log.e("DB ERROR", e.toString()); e.printStackTrace(); } } /********************************************************************** * UPDATING A ROW IN THE DATABASE TABLE * * This is an example of how to update a row in the database table using * this class. You should edit this method to suit your needs. * * @param rowID * the SQLite database identifier for the row to update. * @param rowStringOne * the new value for the row's first column * @param rowStringTwo * the new value for the row's second column */ public void updateRow(long rowID, String rowStringOne, String rowStringTwo, String qty) { // this is a key value pair holder used by android's SQLite functions ContentValues values = new ContentValues(); values.put(TABLE_ROW_ONE, rowStringOne); values.put(TABLE_ROW_TWO, rowStringTwo); values.put(TABLE_ROW_THREE, qty); // ask the database object to update the database row of given rowID try { db.update(TABLE_NAME, values, TABLE_ROW_ID + "=" + rowID, null); } catch (Exception e) { Log.e("DB Error", e.toString()); e.printStackTrace(); } } /********************************************************************** * RETRIEVING A ROW FROM THE DATABASE TABLE * * This is an example of how to retrieve a row from a database table using * this class. You should edit this method to suit your needs. * * @param rowID * the id of the row to retrieve * @return an array containing the data from the row */ public ArrayList<Object> getRowAsArray(long rowID) { // create an array list to store data from the database row. // I would recommend creating a JavaBean compliant object // to store this data instead. That way you can ensure // data types are correct. ArrayList<Object> rowArray = new ArrayList<Object>(); Cursor cursor; try { // this is a database call that creates a "cursor" object. // the cursor object store the information collected from the // database and is used to iterate through the data. cursor = db.query(TABLE_NAME, new String[] { TABLE_ROW_ID, TABLE_ROW_ONE, TABLE_ROW_TWO, TABLE_ROW_THREE }, TABLE_ROW_ID + "=" + rowID, null, null, null, null, null); // move the pointer to position zero in the cursor. cursor.moveToFirst(); // if there is data available after the cursor's pointer, add // it to the ArrayList that will be returned by the method. if (!cursor.isAfterLast()) { do { rowArray.add(cursor.getLong(0)); rowArray.add(cursor.getString(1)); rowArray.add(cursor.getString(2)); rowArray.add(cursor.getString(3)); } while (cursor.moveToNext()); } // let java know that you are through with the cursor. cursor.close(); } catch (SQLException e) { Log.e("DB ERROR", e.toString()); e.printStackTrace(); } // return the ArrayList containing the given row from the database. return rowArray; } /********************************************************************** * RETRIEVING ALL ROWS FROM THE DATABASE TABLE * * This is an example of how to retrieve all data from a database table * using this class. You should edit this method to suit your needs. * * the key is automatically assigned by the database */ public ArrayList<ArrayList<Object>> getAllRowsAsArrays() { // create an ArrayList that will hold all of the data collected from // the database. ArrayList<ArrayList<Object>> dataArrays = new ArrayList<ArrayList<Object>>(); // this is a database call that creates a "cursor" object. // the cursor object store the information collected from the // database and is used to iterate through the data. Cursor cursor; try { // ask the database object to create the cursor. cursor = db.query(TABLE_NAME, new String[] { TABLE_ROW_ID, TABLE_ROW_ONE, TABLE_ROW_TWO, TABLE_ROW_THREE }, null, null, null, null, null); // move the cursor's pointer to position zero. cursor.moveToFirst(); // if there is data after the current cursor position, add it // to the ArrayList. if (!cursor.isAfterLast()) { do { ArrayList<Object> dataList = new ArrayList<Object>(); dataList.add(cursor.getLong(0)); dataList.add(cursor.getString(1)); dataList.add(cursor.getString(2)); dataList.add(cursor.getString(3)); dataArrays.add(dataList); } // move the cursor's pointer up one position. while (cursor.moveToNext()); } } catch (SQLException e) { Log.e("DB Error", e.toString()); e.printStackTrace(); } // return the ArrayList that holds the data collected from // the database. return dataArrays; } /********************************************************************** * THIS IS THE BEGINNING OF THE INTERNAL SQLiteOpenHelper SUBCLASS. * * I MADE THIS CLASS INTERNAL SO I CAN COPY A SINGLE FILE TO NEW APPS AND * MODIFYING IT - ACHIEVING DATABASE FUNCTIONALITY. ALSO, THIS WAY I DO NOT * HAVE TO SHARE CONSTANTS BETWEEN TWO FILES AND CAN INSTEAD MAKE THEM * PRIVATE AND/OR NON-STATIC. HOWEVER, I THINK THE INDUSTRY STANDARD IS TO * KEEP THIS CLASS IN A SEPARATE FILE. *********************************************************************/ /** * This class is designed to check if there is a database that currently * exists for the given program. If the database does not exist, it creates * one. After the class ensures that the database exists, this class will * open the database for use. Most of this functionality will be handled by * the SQLiteOpenHelper parent class. The purpose of extending this class is * to tell the class how to create (or update) the database. * * @author Randall Mitchell * */ private class CustomSQLiteOpenHelper extends SQLiteOpenHelper { public CustomSQLiteOpenHelper(Context context) { super(context, DB_NAME, null, DB_VERSION); } @Override public void onCreate(SQLiteDatabase db) { // This string is used to create the database. It should // be changed to suit your needs. String newTableQueryString = "create table " + TABLE_NAME + " (" + TABLE_ROW_ID + " integer primary key autoincrement not null," + TABLE_ROW_ONE + " text," + TABLE_ROW_TWO + " text" + TABLE_ROW_THREE + " text" + ");"; // execute the query string to the database. db.execSQL(newTableQueryString); String newTableQueryString2 = "alter table " + TABLE_NAME + " ADD COLUMN " + TABLE_ROW_THREE + " text"; // execute the query string to the database. db.execSQL(newTableQueryString2); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // NOTHING TO DO HERE. THIS IS THE ORIGINAL DATABASE VERSION. // OTHERWISE, YOU WOULD SPECIFIY HOW TO UPGRADE THE DATABASE. } } }

Answer 2

Karan我相信你提供的表名i / o_register创建问题只是更改表名并且不在表名中包含'/'然后一切都会正常工作。您的创建查询也没有在Sqlite for Windows上运行。

Answer 3

从表名中删除/，或者将表名始终放在反引号中：

sqlite> create table foo/bar(baz);
Error: near "/": syntax error
sqlite> create table `foo/bar`(baz);
sqlite>

Answer 4

增加db版本。永远有效。

无法在数据库中创建多个表

4 个答案: