Sort search results exclusively by date.

I think I was initially lured into searching by rank because it gives
the illusion of providing the "best match". However, in practice, FTS
never gives back "bad" matches with low ranks -- all of the results it
returns will contain your query in some form (most commonly a direct
substring, but they do take some liberties if you have multiple tokens
in your queries). Given that, in general, more recent search results are
in fact more relevant, we can sort by date exclusively and get a better
ordering overall.

src/org/thoughtcrime/securesms/database/SearchDatabase.java

@@ -56,8 +56,7 @@ public class SearchDatabase extends Database {
         ThreadDatabase.TABLE_NAME + "." + ThreadDatabase.ADDRESS + ", " +
         "snippet(" + SMS_FTS_TABLE_NAME + ", -1, '', '', '...', 7) AS " + SNIPPET + ", " +
         SmsDatabase.TABLE_NAME + "." + SmsDatabase.DATE_RECEIVED + " AS " + MmsSmsColumns.NORMALIZED_DATE_RECEIVED + ", " +
-        MmsSmsColumns.THREAD_ID + ", " +
+        MmsSmsColumns.THREAD_ID + " " +
-        "bm25(" + SMS_FTS_TABLE_NAME + ") AS " + RANK + " " +
       "FROM " + SmsDatabase.TABLE_NAME + " " +
       "INNER JOIN " + SMS_FTS_TABLE_NAME + " ON " + SMS_FTS_TABLE_NAME + "." + ID + " = " + SmsDatabase.TABLE_NAME + "." + SmsDatabase.ID + " " +
       "INNER JOIN " + ThreadDatabase.TABLE_NAME + " ON " + SmsDatabase.TABLE_NAME + "." + MmsSmsColumns.THREAD_ID + " = " + ThreadDatabase.TABLE_NAME + "." + ThreadDatabase.ID + " " +
@@ -67,13 +66,12 @@ public class SearchDatabase extends Database {
         ThreadDatabase.TABLE_NAME + "." + ThreadDatabase.ADDRESS + ", " +
         "snippet(" + MMS_FTS_TABLE_NAME + ", -1, '', '', '...', 7) AS " + SNIPPET + ", " +
         MmsDatabase.TABLE_NAME + "." + MmsDatabase.DATE_RECEIVED + " AS " + MmsSmsColumns.NORMALIZED_DATE_RECEIVED + ", " +
-        MmsSmsColumns.THREAD_ID + ", " +
+        MmsSmsColumns.THREAD_ID + " " +
-        "bm25(" + MMS_FTS_TABLE_NAME + ") AS " + RANK + " " +
       "FROM " + MmsDatabase.TABLE_NAME + " " +
       "INNER JOIN " + MMS_FTS_TABLE_NAME + " ON " + MMS_FTS_TABLE_NAME + "." + ID + " = " + MmsDatabase.TABLE_NAME + "." + MmsDatabase.ID + " " +
       "INNER JOIN " + ThreadDatabase.TABLE_NAME + " ON " + MmsDatabase.TABLE_NAME + "." + MmsSmsColumns.THREAD_ID + " = " + ThreadDatabase.TABLE_NAME + "." + ThreadDatabase.ID + " " +
       "WHERE " + MMS_FTS_TABLE_NAME + " MATCH ? " +
-      "ORDER BY rank ASC, " + MmsSmsColumns.NORMALIZED_DATE_RECEIVED + " DESC " +
+      "ORDER BY " + MmsSmsColumns.NORMALIZED_DATE_RECEIVED + " DESC " +
       "LIMIT 500";
 
   public SearchDatabase(@NonNull Context context, @NonNull SQLCipherOpenHelper databaseHelper) {