Question

仅当该房间在两个日期之间有保留（prenotazione）时，我才想打印该房间的编号（节），以便在设置带有结果的变量时在php中显示错误消息。问题是我的查询似乎要检查是否有房间在这些日期之间设置了保留，并始终提供所请求的任何房间的输出。

SELECT stanze.num_stanza 
FROM stanze, prenotazioni
WHERE prenotazioni.num_stanza=stanze.num_stanza
  AND prenotazioni.check_in 
    BETWEEN '20190615' 
    AND '20190620' 
  OR prenotazioni.check_out
    BETWEEN '20190615'
    AND '20190620'
AND stanze.num_stanza='100'

Answer 1

通常，像x OR y AND z这样的WHERE子句并不是很好。尝试（x或y）和z。否则，如果x为true，则无论z是什么，它都会选择。

例如

WHERE prenotazioni.num_stanza = stanze.num_stanza 
  AND (prenotazioni.check_in BETWEEN '20190615' AND '20190620' OR prenotazioni.check_out BETWEEN '20190615' AND '20190620')
  AND stanze.num_stanza = '100'

Answer 2

不清楚您想要的是什么-全部重叠或部分重叠。

无论哪种方式，您都可以使用EXISTS。以下是部分重叠的信息：

SELECT s.num_stanza
FROM stanze s
WHERE EXISTS (SELECT 1
              FROM prenotazioni p
              WHERE p.num_stanza = s.num_stanza AND 
                    p.check_in < '20190620' AND
                    p.check_out >= '20190615'  
             ) AND
     s.num_stanza = 100  -- looks like number so it probably is

查询总是给出结果，尽管不应该

2 个答案: