sql - case 構文を使用した where 句の日付型

Question

SELECT *
  FROM orders do
 WHERE (CASE TO_CHAR(sysdate,'D')
        WHEN '1'    THEN do.create_date=sysdate
        WHEN '2'    THEN do.create_date BETWEEN sysdate-1 AND sysdate
        WHEN '3'    THEN do.create_date BETWEEN sysdate-2 AND sysdate
        WHEN '4'    THEN do.create_date BETWEEN sysdate-3 AND sysdate
        WHEN '5'    THEN do.create_date BETWEEN sysdate-4 AND sysdate
        WHEN '6'    THEN do.create_date BETWEEN sysdate-5 AND sysdate
        WHEN '7'    THEN do.create_date BETWEEN sysdate-6 AND sysdate
        END)

これの何が問題なのですか？以下のエラーメッセージが表示されます

Error Msg : 
ORA-00905: missing keyword
00905. 00000 -  "missing keyword"
*Cause:    
*Action:
Error at Line: 46 Column: 37