Write SQL query to solve given problem: How much did the win rate increase for the team after getting the No.1 NBA draft pick in the 2003 season than previous season?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT (CAST(SUM(CASE WHEN T1.year = 2004 THEN T1.won ELSE 0 END) AS REAL) / SUM(CASE WHEN T1.year = 2004 THEN T1.won + T1.lost ELSE 0 END)) - (CAST(SUM(CASE WHEN T1.year = 2003 THEN T1.won ELSE 0 END) AS REAL) / SUM(CASE WHEN T1.year = 2003 THEN T1.won + T1.lost ELSE 0 END)) FROM teams AS T1 INNER JOIN draft AS T2 ON T1.tmID = T2.tmID WHERE T2.draftRound = 1 AND T2.draftYear = 2003