SQLite: Obtaining total of all values in one column

问题

I want to create a Query that will give the total of all values in a single column of my SQLite datase.

I want this query to be within a method that returns the total as an int so that I can then further process it within a different activity.

How can I do so?

I have already created similar methods within my Database helper class (see below), but I do not know how to implement a query within SQLite to give the total.

Declaration and creation of database in Databasehelper: (the column i want the total for is COL_MED)

public class DatabaseHelper extends SQLiteOpenHelper {

    // Database Version
    private static final int DATABASE_VERSION = 10;

    // Database Name
    private final static String DATABASE_NAME = "MeditationDatabase";

    // Contacts table name
    private static final String TABLE_SCORE = "scores";

    // Contacts Table Columns names
    private static final String COL_SESSION = "sessionid";
    private static final String COL_GAMETITLE = "game";
    private static final String COL_NAME = "name";
    private static final String COL_MED = "avgmeditation";
    private static final String COL_MAX = "maxmeditation";
    private static final String COL_AVGATT = "avgattention";
    private static final String COL_MAXATT = "maxattention";
    private static final String COL_SCORE = "score";
    private static final String COL_DATE = "date";

    /**
     * Constructor
     * 
     * @param context
     */
    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    /**
     * Method that creates the database
     */
    @Override
    public void onCreate(SQLiteDatabase db) {

        String CREATE_TABLE_SCORE = "CREATE TABLE " + TABLE_SCORE + "(" + COL_SESSION
                + " STRING PRIMARY KEY, " + COL_GAMETITLE + " STRING, "  + COL_NAME + " STRING, " + COL_MED + " INTEGER, "
                 + COL_MAX + " INTEGER, " + COL_AVGATT + " INTEGER, " + COL_MAXATT + " INTEGER, "  + COL_SCORE +  " INTEGER, " + COL_DATE + " STRING " + ")";
        db.execSQL(CREATE_TABLE_SCORE);

    }

Potentially similar method that returns the number of entries in the DB:

public int getTotalGamesPlayed() {
    SQLiteDatabase db = this.getWritableDatabase();
    try {
        return (int)DatabaseUtils.queryNumEntries(db, TABLE_SCORE);
    } finally {
        db.close();
    }
}

EDIT:

Is this the correct query:

String query = "SELECT SUM(COL_MED) FROM " + TABLE_SCORE;

回答1:

Read the documentation; you can use either sum() or total().

The name of the column is not COL_MED; that is the name of the symbol whose value is the name of the column. Like TABLE_SCORE, you would have to insert its value into the SQL query:

int getSumOfAllAvgMeditations() {
    SQLiteDatabase db = getWritableDatabase();
    try {
        String sql = "SELECT TOTAL(" + COL_MED + ") FROM " + TABLE_SCORE;
        return (int)DatabaseUtils.longForQuery(db, sql, null);
    } finally {
        db.close();
    }
}

来源：https://stackoverflow.com/questions/25068254/sqlite-obtaining-total-of-all-values-in-one-column

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android

sql

sqlite