Add some indexes to SQLite tables

Added LOCATION_KEY index bath weather_values and weather_conditions tables.
LOCATION_KEY is used selects/joins with both tables.

In example case this has no real performance effect,
but it's always good habit to have indexes for most commonly used queries.

ex/WeatherServiceProvider/src/vandy/mooc/provider/WeatherDatabaseHelper.java

@@ -63,6 +63,19 @@ public class WeatherDatabaseHelper extends SQLiteOpenHelper {
         + WeatherContract.WeatherValuesEntry.COLUMN_EXPIRATION_TIME 
         + " REAL)";
 
+    /**
+     * index for  LOCATION_EKY 
+     */
+
+    private static final String CREATE_INDEX_WEATHER_VALUES_LOCATION_KEY_IDX =
+        "CREATE INDEX  " + WeatherContract.WeatherValuesEntry.WEATHER_VALUES_TABLE_NAME +  "_" + WeatherContract.WeatherValuesEntry.COLUMN_LOCATION_KEY  + "_idx" 
+        + " ON "
+        + WeatherContract.WeatherValuesEntry.WEATHER_VALUES_TABLE_NAME
+        + "(" 
+        + WeatherContract.WeatherValuesEntry.COLUMN_LOCATION_KEY 
+        + ")";
+
+
     /**
      * SQL statement used to create the Weather Conditions table.
      */
@@ -83,6 +96,20 @@ public class WeatherDatabaseHelper extends SQLiteOpenHelper {
         + WeatherContract.WeatherConditionsEntry.COLUMN_ICON
         + " TEXT) ";
 
+
+    /**
+     * index for weather conditions LOCATION_KEY, which is used for join queries to 
+     */
+
+
+    private static final String CREATE_INDEX_WEATHER_CONDITIONS_LOCATION_KEY_IDX = 
+        "CREATE INDEX  " + WeatherContract.WeatherConditionsEntry.WEATHER_CONDITIONS_TABLE_NAME +  "_" + WeatherContract.WeatherConditionsEntry.COLUMN_LOCATION_KEY + "_idx" 
+        + " ON "
+        + WeatherContract.WeatherConditionsEntry.WEATHER_CONDITIONS_TABLE_NAME
+        + "(" 
+        + WeatherContract.WeatherConditionsEntry.COLUMN_LOCATION_KEY 
+        + ")";
+
      /**
      * Constructor - initialize database name and version, but don't
      * actually construct the database (which is done in the
@@ -109,6 +136,10 @@ public void onCreate(SQLiteDatabase db) {
         // Create the tables.
         db.execSQL(CREATE_TABLE_WEATHER_VALUES);
         db.execSQL(CREATE_TABLE_WEATHER_CONDITIONS);
+
+        // create index for LOCATION_KEY in both tables. (used in most queries)
+        db.execSQL(CREATE_INDEX_WEATHER_VALUES_LOCATION_KEY_IDX);
+        db.execSQL(CREATE_INDEX_WEATHER_CONDITIONS_LOCATION_KEY_IDX);
     }
 
     /**