Question

我构建了一个SQL查询来获取所有可用于出租且未预订的select property.address from (period join booking on period.propertyid = booking.propertyid) join property on period.propertyid = property.id where period.type = 'available' AND period.end >= TO_DATE('2016-01-25', 'YYYY-MM-DD') AND period.start <= TO_DATE('2016-01-20', 'YYYY-MM-DD') AND ( booking.start > TO_DATE('2016-01-25', 'YYYY-MM-DD') OR booking.start < TO_DATE('2016-01-20', 'YYYY-MM-DD') ) AND ( booking.end > TO_DATE('2016-01-25', 'YYYY-MM-DD') OR booking.end < TO_DATE('2016-01-20', 'YYYY-MM-DD') );地址：

period join booking on period.propertyid = booking.propertyid

但由于periods，它不会查询properties表中不存在的booking（公寓）的booking。

如何加入periods表，以便仍然查询所有{{1}}？

Answer 1

使用LEFT JOIN：

select property.address
  from (
    period 
    left join booking on period.propertyid = booking.propertyid) 
...

Answer 2

SELECT property.address
FROM property
LEFT JOIN period  ON period.propertyid = property.id
LEFT JOIN booking ON period.propertyid = booking.propertyid
WHERE period.type = 'available'
AND period.end   >= '2016-01-25'
AND period.start <= '2016-01-20'
AND (booking.start > '2016-01-25' OR booking.start < '2016-01-20')
AND (booking.end   > '2016-01-25' OR booking.end   < '2016-01-20')

将表连接到另一行后查询表的每一行

2 个答案: