Question

I have this query

public Cursor control(String a){
    return mDb.query(ProductsMetaData.C_TABLE, null,ProductsMetaData.A+ "=?" , new String[] {String.valueOf(a)},  null, null, null, null);
}

and it works.
Now I need to implement the “AND” because I want only rows where ProductsMetaData.A = a and ProductsMetaData.B = b but what I’m doing doesn’t work.

public Cursor control(String a, String b){
    return mDb.query(ProductsMetaData.C_TABLE, null,ProductsMetaData.A+ "=?" + ProductsMetaData.B + "=?" , new String[] {String.valueOf(a), String.valueOf(b)},  null, null, null, null);
}

Could someone help me?

Answer 1

You simply need to add the AND keyword:

ProductsMetaData.A + "=? AND " + ProductsMetaData.B + "=?"

Also your parameters a and b are already Strings, so you can simply use:

new String[] {a, b}

---

Can I ask you how can I implement update and delete too?

Delete is easy enough:

public int delete(String a, String b) {
    return mDb.delete(ProductsMetaData.C_TABLE, ProductsMetaData.A + "=? AND " + ProductsMetaData.B + "=?", new String[] {a, b});
}

Updates require a ContentValues object:

public int update(String newA, String newB, String oldA, String oldB) {
    ContentValues values = new ContentValues();
    values.put(ProductsMetaData.A, newA);
    values.put(ProductsMetaData.B, newB);
    return mDb.update(ProductsMetaData.C_TABLE, values, ProductsMetaData.A + "=? AND " + ProductsMetaData.B + "=?", new String[] {oldA, oldB});
}

One final note, if you find yourself using ProductsMetaData.A + "=? AND " + ProductsMetaData.B + "=?" numerous times, you can save it in a static final variable just like C_TABLE, A, and B:

private static final String WHERE_A_B = ProductsMetaData.A + "=? AND " + ProductsMetaData.B + "=?";