Question

是否可以使用结果＆＃34;列＆＃34;来自同一查询中另一个if条件的if条件？我想一次获取所有文档相关数据。

SELECT d.id, d.filename, 

IF(d.document_valid_until_further_notice = 0,
    IF(d.document_valid_until = "0000-00-00", 
        DATE_ADD(d.document_date, INTERVAL 12 MONTH),
        d.document_valid_until
    ), "0000-00-00"
) AS calculated_valid_until_date,

IF(calculated_valid_until_date != "0000-00-00", 
    DATE_SUB(calculated_valid_until_date, INTERVAL 8 WEEK, 
    "0000-00-00"
) AS calculated_alert_expiring_date, 
IF(calculated_valid_until_date > CURDATE() AND calculated_valid_until_date != "0000-00-00", 1, 0) AS expired FROM documents AS d WHERE 1 ORDER BY d.document_date DESC';

现在，＆＃34; calculated_valid_until_date＆＃34;正确地出来，例如， 2015-10-20，但我不能在以下if语句中使用该值。有没有@ -sign。（@calculated_valid_until_date）。有没有办法或者我必须使用单独的查询或在客户端进行此操作？

感谢您的任何想法！

Answer 1

将计算出的字段包装到派生表中，然后在此派生表的外部选择中引用这些计算以继续计算：

SELECT x.id, x.filename, 
  x.calculated_valid_until_date, 
  x.calculated_alert_expiring_date,
  -- Use the derived table to do the second round of calculations 
  IF(x.calculated_valid_until_date > CURDATE() 
    AND x.calculated_valid_until_date != "0000-00-00", 1, 0) AS expired
FROM
-- Project the first round of calculations into a derived table
(SELECT
  d.id, d.filename, d.document_date,

 IF(d.document_valid_until = '0000-00-00', DATE_ADD(d.document_date, INTERVAL 12 MONTH),
 d.document_valid_until) AS calculated_valid_until_date,

IF(d.calculated_valid_until_date != '0000-00-00', 
    DATE_SUB(d.calculated_valid_until_date, INTERVAL 8 WEEK), 
    '0000-00-00') AS calculated_alert_expiring_date

  FROM documents AS d     
) x
WHERE 1 = 1
ORDER BY x.document_date DESC;

SqlFiddle here

Answer 2

SELECT x.id, x.filename, 
  x.calculated_valid_until_date,
  IF(x.calculated_valid_until_date < CURDATE() AND x.calculated_valid_until_date != "0000-00-00", 1, 0) AS expired, IF(x.calculated_valid_until_date != '0000-00-00', 
    DATE_SUB(x.calculated_valid_until_date, INTERVAL 8 WEEK), '0000-00-00') AS calculated_alert_expiring_date 
FROM
(SELECT
  d.id, d.filename, d.document_date, d.calculated_alert_expiring_date, 

 IF(d.document_valid_until = '0000-00-00', DATE_ADD(d.document_date, INTERVAL 12 MONTH),
 d.document_valid_until) AS calculated_valid_until_date

  FROM documents AS d     
) x
WHERE 1 = 1
ORDER BY x.document_date DESC

CREATE TABLE文档（ id INT， filename VARCHAR（50）， document_valid_until_further_notice TINYINT（1）， document_valid_until_date日期， document_date DATE， document_valid_until日期， calculated_valid_until_date日期， calculated_alert_expiring_date日期）;

这就是我的工作方式。我没有第一次看到小提琴，所以我没有意识到我必须为＆＃34; calculated_valid_until_date＆＃34;创建表格列。和＆＃34; calculated_alert_expiring_date＆＃34;。

但无论如何，它现在正在发挥作用。谢谢！

mysql，在以下if条件中使用if条件的结果

2 个答案: