使用 UNION 将两个语句与 LIMITS 合并

Question

有没有办法将这两个语句合并为一个而不会出现重复条目​​？

SELECT * FROM Seq where JULIANDAY('2012-05-25 19:02:00')<=JULIANDAY(TimeP) 
         order by TimeP limit 50

SELECT * FROM Seq where JULIANDAY('2012-05-29 06:20:50')<=JULIANDAY(TimeI)  
         order by TimeI limit 50

SQLITE 不支持我的第一个明显尝试（语法错误：限制子句应该在 UNION 之后而不是之前）：

SELECT * FROM Seq where JULIANDAY('2012-05-25 19:02:00')<=JULIANDAY(TimeP) 
         order by TimeP limit 50
UNION
SELECT * FROM Seq where JULIANDAY('2012-05-29 06:20:50')<=JULIANDAY(TimeI)
         order by TimeI limit 50

Answer 1

使用子查询并在其中执行限制。

SELECT  *
FROM    (   SELECT  * 
            FROM    Seq 
            WHERE   JULIANDAY('2012-05-25 19:02:00') <= JULIANDAY(TimeP) 
            ORDER BY TimeP
            LIMIT 50
        )
UNION
SELECT  *
FROM    (   SELECT  * 
            FROM    Seq 
            WHERE   JULIANDAY('2012-05-29 06:20:50') <= JULIANDAY(TimeI) 
            ORDER BY TimeI
            LIMIT 50
        )

Answer 2

查询分阶段处理：

1. FROM 子句和所有连接；
2. WHERE 子句和所有谓词。因此，如果您想在结果集中查看NULL 值，则永远不要在WHERE 部分中过滤OUTER-joined 表列，因为这会将您的查询变成INNER 连接；
3. GROUP BY 和 HAVING 子句；
4. 查询组合：UNION、INTERSECT、EXCEPT 或 MINUS
5. ORDER BY
6. LIMIT

因此，正如其他人指出的那样，使用 ORDER BY 和 LIMIT before UNION 子句在语法上是错误的。你应该使用子查询：

SELECT *
  FROM (SELECT * FROM Seq
         WHERE JULIANDAY('2012-05-25 19:02:00') <= JULIANDAY(TimeP) 
         ORDER BY TimeP LIMIT 50) AS tab1
UNION
SELECT *
  FROM (SELECT * FROM Seq
         WHERE JULIANDAY('2012-05-29 06:20:50') <= JULIANDAY(TimeI)  
         ORDER BY TimeI LIMIT 50) AS tab2;

Answer 3

           SELECT * from 
           (SELECT * 
           FROM Seq 
           where JULIANDAY('2012-05-25 19:02:00')<=JULIANDAY(TimeP) 
           order by TimeP limit 50)
           UNION
           SELECT * from 
           (SELECT * 
           FROM Seq 
           where JULIANDAY('2012-05-29 06:20:50')<=JULIANDAY(TimeI)
           order by TimeI limit 50)

这应该可以解决问题