Xcode, iphone, Sqlite, need a sign function for group by?

Question

I need an sql sign function for my group by query to group positive and negative amounts.

Unfortunately sqlite doesn't include one.

Can anyone suggest a workaround ? or how to ad one to work with the libsqlite3.dylib framework used in xcode ?

My query is quite complicated

select fcid, sum(price), (select sum(price) from tmp b where ((b.due < a.due) 
or ((b.due = a.due) and (b.pid <= a.pid)))) as accumulated_price from tmp a 
where due >= '2011-01-25' and due < '2011-02-24' and price <> 0 group by fcid 
order by due, pid;

What I'm trying to do, is a group on sign(price) so I get two result and negative value and a positive value. These will represent total expenses and total income.

Would like to have added these tags (but I'm not allowed to create new ones libsqlite3.dylib libsqlite3)

Answer 1

Don't know if it's your best choice, but you can try:

select your_val > 0, sum(aggregated_value)
  from your_table
 group by your_val > 0;

This way, you should have 0 for ZERO or negative values and 1 for positive values.

UPDATE: If fcid is the field you need the sign for, you can try:

select fcid > 0, sum(price), 
       (
         select sum(price) 
           from tmp b
          where ((b.due < a.due) or ((b.due = a.due) and (b.pid <= a.pid)))
       ) as accumulated_price 
  from tmp a 
 where due >= '2011-01-25' 
   and due < '2011-02-24' 
   and price <> 0 
 group by fcid > 0;

Note that your order by clause is useless since you are grouping your results anyway.

Answer 2

You should just create your own sign function. See Create or Redefine SQL Functions .

Register a function using sqlite3_create_function :

sqlite3_create_function( db, "sign", 1, SQLITE_ANY, NULL, signFunc,
                         NULL, NULL);

Then implement signFunc in C.

static void signFunc(sqlite3_context *c, int argCount, sqlite3_value **args) {
    if ( argCount != 1 ) {
        sqlite3_result_null( c );
        return;
    }

    switch ( sqlite3_value_type( args[0] ) ) {
        case SQLITE_INTEGER: {
            sqlite3_int64 asInt = sqlite3_value_int64( args[0] );
            sqlite3_int64 sign = asInt < 0 ? -1 : (asInt > 0 ? 1 : 0);
            sqlite3_result_int64( c, sign );
            break;
        }
        case SQLITE_FLOAT: {
            double asDouble = sqlite3_value_double( args[0] );
            sqlite3_int64 sign = asDouble < 0 ? -1 : (asDouble > 0 ? 1 : 0);
            sqlite3_result_double( c, sign );
            break;
        }
        case SQLITE_NULL:
        default: {
            sqlite3_result_null( c );
            break;
        }
    }
}