如何在onUpgrade中添加列并将现有行设置为特定值？

Question

How do I add a column in DatabaseHelper onUpgrade and set pre-existing rows to a particular value?

I tried:

    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    ...
       if (oldVersion < 2) {
          db.execSQL("ALTER TABLE " + MyTableName + " ADD COLUMN "
              + MyNewColumn + " TEXT;");      
          db.execSQL("UPDATE " + MyTableName  + " SET " +
               MyNewColumn  + "=" + "value for existing;");
       }
    }

But I don't think the alter has been committed yet because it says the column doesn't exist. Any suggestion?

Edit: Added some more surrounding code

Edit: My mistake. I was just missing a quote around the value part and the error about no column threw me off, but the issue was it was looking for the column for the value I had used without the quote.

Answer 1

It's not as simple adding a column as you have shown as the onUpgrade will run every time you upgrade the database and adding the column a second time will fail... If you wish to do it quick and dirty you can wrap it in a try catch

try {
    db.execSQL("ALTER TABLE sometable ADD COLUMN newcolumn integer");   
}
catch(Exception e) {
    e.printStackTrace();
}

A better way is to move all of the data out of the table into a temp table, drop and re-create the table and put your data back in. Here is an example from something I've used before

//Update old Table
        if(DBVER< 1060){

            List<String> columns = DB.GetColumns(db, "listitems");
            db.execSQL("ALTER table listitems RENAME TO 'temp_listitems); ") ;
            String tblListItems = "create table if not exists listitems " +
                    "(id integer primary key autoincrement, " +
                    "listid integer, " +
                    "itemid integer, " +
                    "qty integer, " +
                    "collected integer, " +
                    "qtytype integer, " +
                    "tabid integer); " ;
            db.execSQL(tblListItems);
            columns.retainAll(DB.GetColumns(db, "listitems"));
            String cols = DB.join(columns, ","); 
            db.execSQL(String.format( "INSERT INTO %s (%s) SELECT %s from temp_%s", "listitems", cols, cols, "listitems"));
            db.execSQL("DROP table 'temp_" + "listitems");



        }

Heres a link http://www.devdaily.com/android/sqlite-alter-table-syntax-examples

Answer 2

 db.execSQL("ALTER TABLE " + MyTableName + " ADD "
           + MyNewColumn + " TEXT;"); 

Try it without Column: Syntax is:

ALTER TABLE [TABLE_NAME] ADD [COLUMN_NAME] DATATYPE