SQLite，表，联接

Question

Android, implementing SQLite

These are the tables i have:

http://postimg.org/image/jafsx39h7/

I have the code:

public String getWorkoutNameInfo() {
    // TODO Auto-generated method stub

    String[] columns = new String[] { KEY_DATE_OF_WORKOUT,
            KEY_WORKOUT_NAME, KEY_DATE };           
    Cursor c = ourDatabase.query(TABLE_DATE_WORKOUT, columns, null, null,           
            null, null, null, null);                    
    String workoutName2 = "";               
    int iWorkoutID = c.getColumnIndex(KEY_WORKOUT_NAME);
    for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
        workoutName2 = workoutName2 + c.getString(iWorkoutID);  

            }

        return workoutName2;

}

This returns workoutName2 which is '2 1 2'

Now i need to look up the value for 2 in my WorkoutTable and return 'Back' and produce 'Back,Chest,Back' so i can out put that onto my screen instead of 2 1 2.

I understand I'll be using a JOIN statement? However i'm having no luck implementing it.

My Table Coding:

// WORKOUT TABLE - COLUMN NAMES
public static final String KEY_WORKOUT = "workout_id";
public static final String STRING_WORKOUT = "workout_name"; 


    // DATE OF WORKOUT TABLE - COLUMN NAMES
public static final String KEY_DATE_OF_WORKOUT = "date_of_workout_id";
public static final String KEY_DATE = "date_of_workout";
public static final String KEY_WORKOUT_NAME = "workout_id";

    //TABLE NAMES
private static final String TABLE_WORKOUT = "WorkoutTable";
private static final String TABLE_DATE_WORKOUT = "DateofWorkout";

Here is my attempt:

public String test(String workoutSelectedNameInfo) {

    // TODO Auto-generated method stub
    String NAMEofWorkout = "";
    open();
    ourDatabase = ourhelper.getReadableDatabase();
    Cursor c = ourDatabase
            .rawQuery(
                    "SELECT * FROM WorkoutTable LEFT JOIN DateofWorkout ON (WorkoutTable.workout_id = DateofWorkout.workout_id)   WHERE workout_id = ?",
                    new String[] { "2" });



    int iDateofWorkoutsWorkoutId = c.getColumnIndex(KEY_WORKOUT_NAME);
    for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
        NAMEofWorkout = NAMEofWorkout + c.getString(iDateofWorkoutsWorkoutId);
    }
    c.close();
    ourDatabase.close();
    System.out.println(NAMEofWorkout);
    return NAMEofWorkout;

}

HOWEVER When it output the 'NameofWorkout' which SHOULD be Chest,Back,Chest i receive nothing at all, absolutely blank.

Answer 1

When I enter your data into a SQLite instance on my machine and then execute your query, I get the following error:

Error: ambiguous column name: workout_id

In the query, changing WHERE workout_id to WHERE DateofWorkout.workout_id makes the error go away.

This problem happens because there are two columns named workout_id in the result, and you must disambiguate your subsequent references. Because of this, you probably must also change

c.getColumnIndex(KEY_WORKOUT_NAME)

to

c.getColumnIndex(TABLE_DATE_WORKOUT + "." + KEY_WORKOUT_NAME)

when you make use of the results later.