顯示今年每月的訪問量

Question

我想顯示今年每月的總訪問量。但以下查詢返回缺少表達式的錯誤代碼。我錯過了什麼？

SELECT CASE 
    WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '),  'mm/dd/yyyy') = 1 THEN 'January ' 
    WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 2 THEN 'February' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 3 THEN 'March' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 4 THEN 'April' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 5 THEN 'May' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 6 THEN 'June' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 7 THEN 'July' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 8 THEN 'August' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 9 THEN 'September' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 10 THEN 'October' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 11 THEN 'November' 
ELSE 'December' 
    END AS "Month " , 
    COUNT(*) AS "Number of visits" 
FROM allrecord where extract(year from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy')= extract(year from date sysdate) 
GROUP BY CASE 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 1 THEN 'January ' 
    WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 2 THEN 'February' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 3 THEN 'March' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 4 THEN 'April' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 5 THEN 'May' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 6 THEN 'June' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 7 THEN 'July' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 8 THEN 'August' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 9 THEN 'September' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 10 THEN 'October' 
WHEN extract(month from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy') = 11 THEN 'November' 

     ELSE 'December' 
      END; 

問一個額外的問題，我正在使用ORacle應用程序構建器創建一個應用程序。但在創建頁面並想要編輯表單中的記錄後，會顯示一條錯誤消息，指出可以提取數據。這是什麼意思？我錯過了什麼步驟？

Answer 1

不甲骨文有一個函數從這樣的日期提取MONTHNAME：

SELECT TO_CHAR(visit_time 'MONTH') as month 
COUNT(*) AS "Number of visits" 
FROM allrecord 
WHERE extract(year from date TO_DATE (TO_CHAR (visit_time, 'mm/dd/yyyy '), 'mm/dd/yyyy')= extract(year from date sysdate) 
GROUP BY TO_CHAR(visit_time 'MONTH') 

Answer 2

這個查詢都可以降低冷凝爲：

select to_char(VISIT_TIME, 'fmMonth') as "Month" 
     ,count(*) as "Number of Visits" 
    from ALLRECORD 
    where extract(year from VISIT_TIME) = extract(year from sysdate) 
group by to_char(VISIT_TIME, 'fmMonth'); 

缺少表達錯誤將有來自將函數中的to_date前面的關鍵字date。這是沒有必要的。你要麼使用：

select extract (year from date '2011-01-01') from sys.dual 

或：

select extract (year from to_date('2011-01-01')) from sys.dual 

但從來沒有：

select extract (year from date to_date('2011-01-01')) from sys.dual