Android / Java：如何在sqlite中获取最后一行的值？

Question

Hello I am using a sqlite database in my android application, and I have question: I am trying to get the last value text(thats the collumn) from the last row from the table TABLE_XYZ... but it does not work.. i am using the following code...what am I doing wrong?

another question is, how can I return two values instead of only one, when I want to get several values from the last row like column text and message?

private static final String KEY_MESSAGE = "message";
private static final String KEY_TEXT = "text";

...

String selectQuery= "SELECT * FROM " + TABLE_XYZ+" ORDER BY column DESC LIMIT 1";
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);
     cursor.close();
    return cursor.getString( cursor.getColumnIndex(KEY_TEXT) ); 

EDIT:

i hade some errors in my Query,, i fixed it, but still have errors:

    String selectQuery= "SELECT * FROM " + TABLE_XYZ +  " ORDER BY " +  KEY_TEXT+ " DESC LIMIT 1";
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);
    String str =  cursor.getString( cursor.getColumnIndex(KEY_TEXT );
    cursor.close();
    return str; 

while debugging I can see that cursor does have the right values inside... but when i try to get the column value with this command "cursor.getString( cursor.getColumnIndex(KEY_TEXT );"... it does not work...

Answer 1

you are closing cursor before getting it's value

try this :

String selectQuery= "SELECT * FROM " + TABLE_XYZ+" ORDER BY column DESC LIMIT 1";
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
String str = "";
if(cursor.moveToFirst())
    str  =  cursor.getString( cursor.getColumnIndex(KEY_TEXT) );
cursor.close();
return str;

Answer 2

From the android documentation: http://developer.android.com/reference/android/database/Cursor.html

abstract void close() Closes the Cursor, releasing all of its resources and making it completely invalid.

You are closing the cursor before returningthe string.

Answer 3

Like @whatever5599451 said you should not close the cursor before you get value. Also try a query like this:

String selectQuery = "SELECT column FROM " + TABLE_XYZ + 
                     " ORDER BY column DESC LIMIT 1";

You can specify the columns also specify to return only 1 row.

This will bring back only the column you are ordering by you can also specify more columns example:

String selectQuery = "SELECT column, column2, column3 FROM " + TABLE_XYZ + 
                     " ORDER BY column DESC LIMIT 1";

* means select all columns

Answer 4

要获取最后一列，请使用该列的名称，而不要使用“ *”（*表示所有字段）

Answer 5

@Steve: do this:

String selectQuery= "SELECT " + KEY_TEXT + " FROM " + TABLE_XYZ + " ORDER BY " + KEY_TEXT+ " DESC LIMIT 1";

then you get just one String with the last record containing just the right column