Question

我想在同一列中创建sql req两次使用order我尝试使用此示例

public static void main(String[] args){
Student student1 = new Student();

但是sql错误表明UNION和ORDER BY的使用不正确

SELECT  titleEN, smallDescriptionEN, StartDate, EndDate
            FROM event
            WHERE EndDate > NOW()
            ORDER BY StartDate ASC

UNION

SELECT  titleEN, smallDescriptionEN, StartDate, EndDate
                FROM event
                WHERE EndDate < NOW()
                ORDER BY StartDate DESC

Answer 1

最后一个Order By足以订购完整的结果集

SELECT titleEN,
       smallDescriptionEN,
       StartDate,
       EndDate
FROM   event
WHERE  EndDate < Now()
UNION
SELECT titleEN,
       smallDescriptionEN,
       StartDate,
       EndDate
FROM   event
WHERE  EndDate > Now()
ORDER  BY StartDate DESC;

Answer 2

假设这只是一个例子，并且假设您的商业案例是合法的，那么这将完全符合您的要求：

DECLARE @tmpAsc AS TABLE (titleEN VARCHAR(MAX), smallDescriptionEN VARCHAR(MAX), 
    StartDate DATETIME, EndDate DATETIME)

INSERT INTO @tmpAsc
SELECT titleEN,
       smallDescriptionEN,
       StartDate,
       EndDate
FROM [EVENT]
WHERE EndDate > GETDATE()
ORDER BY StartDate DESC

DECLARE @tmpDesc AS TABLE (titleEN VARCHAR(MAX), smallDescriptionEN VARCHAR(MAX), 
    StartDate DATETIME, EndDate DATETIME)

INSERT INTO @tmpDesc
SELECT titleEN,
       smallDescriptionEN,
       StartDate,
       EndDate
FROM   [EVENT]
WHERE  EndDate < GETDATE()
ORDER  BY StartDate DESC;

SELECT * FROM @tmpAsc
UNION ALL
SELECT * FROM @tmpDesc

Answer 3

如前所述，联合查询只有一个ORDER BY子句。如果要对这种方式进行排序，则需要一个带有CASE结构的子句：

SELECT  titleEN, smallDescriptionEN, StartDate, EndDate
FROM event
WHERE EndDate > NOW()
UNION ALL
SELECT  titleEN, smallDescriptionEN, StartDate, EndDate
FROM event
WHERE EndDate < NOW()
ORDER BY 
  CASE WHEN EndDate > NOW() THEN 1 ELSE 2 END -- "after now" before "before now"
  CASE WHEN EndDate < NOW() THEN StartDate ELSE NULL END DESC
  CASE WHEN EndDate > NOW() THEN StartDate ELSE NULL END ASC;

或者简单地说：

select  titleen, smalldescriptionen, startdate, enddate
from event
where enddate <> now()
order by (enddate < now()), abs(timestampdiff(second, now(), startdate)) desc;

日期/时间操作是特定于dbms的（就此而言是布尔表达式）。这适用于MySQL。

如何在同一列中创建2个订单

3 个答案: