Question

我看了搜索但找不到答案。如果在houses_availability中没有匹配的记录，我需要在houses_houses中查看记录。我知道它与IS NULL有关，但我尝试的都失败了。请帮忙。

SELECT 
    houses_houses.*, 
    houses_availability.from_date 
FROM 
    houses_houses 
LEFT JOIN 
    houses_availability ON houses_houses.sid=houses_availability.housesid 
WHERE 
    houses_availability.from_date>='2015-09-05' 
AND 
    houses_availability.until_date<'2015-09-11'  
ORDER BY houses_houses.sid LIMIT 0, 9

Answer 1

在WHERE子句中的LEFT OUTER JOINed表中检查NULL： -

SELECT 
    houses_houses.*, 
    houses_availability.from_date 
FROM houses_houses 
LEFT JOIN houses_availability 
ON houses_houses.sid=houses_availability.housesid 
AND houses_availability.from_date>='2015-09-05' 
AND houses_availability.until_date<'2015-09-11'  
WHERE houses_availability.housesid IS NULL
ORDER BY houses_houses.sid LIMIT 0, 9

重要的是要注意，不应该检查WHERE子句中LEFT OUTER JOINed表中的任何列，因为这会在连接之后排除整行，而不是在连接之前排除LEFT OUTER JOINed表行。因此，检查ON子句中的日期范围

Answer 2

您需要在JOIN .. ON子句中包含您的houses_availability条件：

SELECT houses_houses.*, houses_availability.from_date 
 FROM houses_houses 
 LEFT JOIN houses_availability ON (houses_houses.sid=houses_availability.housesid AND houses_availability.from_date>='2015-09-05' 
  AND houses_availability.until_date<'2015-09-11')
 WHERE 
  houses_availability.housesid is null
ORDER BY houses_houses.sid LIMIT 0, 9

如果连接表中没有记录，则mysql结果

2 个答案: