我在SqLite中删除表时遇到问题 .
如果我使用 -
db.delete(TABLE_NAME,null,null);
删除表的内容但仍保留列名 . 如何删除列名?
我也尝试了db.execSQL(“DROP TABLE IF EXISTS”TABLE_NAME“表的名称”);
但它根本不起作用 .
如何以编程方式删除整个表,或者有没有办法删除整个数据库而不需要通过代码生根(否则我们得到“权限被拒绝”错误)?
以下是处理onCreate,创建和删除表的代码的一部分 .
package com.example.appchecker;
import java.io.File;
import com.example.appchecker.FeedReaderContract.CycDetails;
import com.example.appchecker.FeedReaderContract.FeedEntry;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class FeedReaderDbHelper2 extends SQLiteOpenHelper {
// If you change the database schema, you must increment the database version.
public static final int DATABASE_VERSION = 1;
public static final String DATABASE_NAME = "final31.db";
public static boolean exists = false;
private static final String TEXT_TYPE = " TEXT";
private static final String COMMA_SEP = ", ";
private static final String SQL_CREATE_ENTRIES =
" CREATE TABLE " +FeedEntry.TABLE_NAME + " (" +
FeedEntry._ID + " INTEGER PRIMARY KEY" + COMMA_SEP +
FeedEntry.COLUMN_NAME_NUMBER + TEXT_TYPE + COMMA_SEP +
FeedEntry.COLUMN_NAME_APP_NAME + TEXT_TYPE + COMMA_SEP +
FeedEntry.COLUMN_NAME_PKG_NAME + TEXT_TYPE +
// Any other options for the CREATE command
");";
private static final String SQL_CREATE_ENTRIES2 =
" CREATE TABLE " +CycDetails.TABLE_NAME + " (" +
CycDetails._ID + " INTEGER PRIMARY KEY" + COMMA_SEP +
CycDetails.COLUMN_NAME_CYCLENAME + TEXT_TYPE + COMMA_SEP +
CycDetails.COLUMN_NAME_DATE + TEXT_TYPE + COMMA_SEP +
CycDetails.COLUMN_NAME_OSVERSION + TEXT_TYPE + COMMA_SEP +
CycDetails.COLUMN_NAME_SWVERSION + TEXT_TYPE +
// Any other options for the CREATE command
");";
private static final String SQL_DELETE_ENTRIES1 =
"DROP TABLE IF EXISTS " + DATABASE_NAME.substring(0,DATABASE_NAME.length()-3)+".Mobile_App_Details";
private static final String SQL_DELETE_ENTRIES2 =
"DROP TABLE IF EXISTS " + DATABASE_NAME.substring(0, DATABASE_NAME.length()-3)+".Cycle_Details";
public FeedReaderDbHelper2(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
db.execSQL(SQL_CREATE_ENTRIES);
db.execSQL(SQL_CREATE_ENTRIES2);
return;
} /*Cursor cursor = db.rawQuery("select DISTINCT tbl_name from sqlite_master where tbl_name = '"+FeedEntry.TABLE_NAME+"'", null);
System.out.println("In on create1") ;
if(cursor==null)
{
System.out.println("In on create") ;
db.execSQL(SQL_CREATE_ENTRIES);
}
else
{
System.out.println("Update phase") ;
exists=true;
}
*/
}
public static void deletetable(SQLiteDatabase db)
{
db.delete(FeedEntry.TABLE_NAME, null, null);
db.delete(CycDetails.TABLE_NAME, null, null);
db.execSQL(SQL_DELETE_ENTRIES1);
db.execSQL(SQL_DELETE_ENTRIES2);
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// This database is only a cache for online data, so its upgrade policy is
// to simply to discard the data and start over
//System.out.println("Update phase") ;
db.execSQL(SQL_DELETE_ENTRIES1);
db.execSQL(SQL_DELETE_ENTRIES2);
//db.delete(FeedEntry.TABLE_NAME, null, null);
onCreate(db);
}
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
onUpgrade(db, oldVersion, newVersion);
}
}
目前我即使在MainActicity中也在on_click中实例化deletetable函数 . Logcat没有显示错误,但是当我打印检索到的列名时,它会打印一些已删除条目的列名 . 我不想要那些专栏 .
而且我没有以任何方式使用升级方法 .
3 回答
您应该更正drop table SQL的语法(DROP TABLE IF EXISTS是两次),没有理由不起作用 .
如果您获得权限被拒绝错误,请确保您正在访问您自己的应用程序的数据库,而不是其他应用程序的数据库 . 如果需要,请在创建数据库时仔细检查是否使用了正确的软件包名称 .
从数据库中删除表 .
db.execSQL(“DROP TABLE IF EXISTS”YOUR_TABLE);
要删除表,只需使用DROP TABLE语句 .
表名应与您在
CREATE TABLE
语句中使用的完全相同 . 在您的情况下,这将是: