android sqlite CREATE TABLE IF NOT NOT EXISTS

Question

在创建新表时遇到一些问题.当我使用CREATE TABLE命令时,我的新表格应该如此形成,但当我退出活动时,应用程序崩溃,我在logcat中获得了一个TABLE ALREADY EXISTS.如果我使用CREATE TABLE IF NOT EXISTS,则不会形成新表,只是将新的数据行添加到上一个表中,并且不会崩溃.这有什么问题？我想添加表没有它给我已经存在,我希望它添加没有它添加行到不同的表.

SqliteHelper类:

public class MySQLiteHelper extends SQLiteOpenHelper {


public static final String TABLE_NAME = MainActivity.NameName;

public static final String COLUMN_ID = "_id";
public static final String COLUMN_COMMENT = "comment";
public static final String COLUMN_LAT = "lat";
public static final String COLUMN_LONG = "long";
public static final String COLUMN_RADI = "radi";
private static final String DATABASE_NAME = "spraylogs.db";
private static final int DATABASE_VERSION = 1;



public static final String NEWTABLE = "CREATE TABLE  "
         + TABLE_COMMENTS + "(" + COLUMN_ID
          + " integer primary key autoincrement, " + COLUMN_COMMENT
          + " text not null," + COLUMN_LAT+ ","  + COLUMN_LONG + "," + COLUMN_RADI +  ");";

public static final String SaveIt = "CREATE TABLE IF NOT EXISTS "
         + TABLE_COMMENTS + "(" + COLUMN_ID
          + " integer primary key autoincrement, " + COLUMN_COMMENT
          + " text not null," + COLUMN_LAT+ ","  + COLUMN_LONG + "," + COLUMN_RADI +  ");";



 MySQLiteHelper(Context context) {
  super(context, context.getExternalFilesDir(null).getAbsolutePath() + "/" + DATABASE_NAME, null, DATABASE_VERSION);
}


@Override
public void onCreate(SQLiteDatabase database) {
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(MySQLiteHelper.class.getName(),
    "Upgrading database from version " + oldVersion + " to "
        + newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + NEWTABLE);

onCreate(db);
 } 

} 

Answer 1

这就是它应该如何运作. CREATE TABLE如果表已经存在,将抛出异常. CREATE TABLE IF NOT EXISTS如果表不存在则创建表,否则忽略该命令.如果要删除旧表,请使用DELETE TABLE IF EXISTS之前CREATE TABLE.如果要更改架构,请使用ALTER TABLE,而不是CREATE TABLE.