按顺序由ASC在底部的空值

我正在写一个SQL查询，将学校表连接到一个分区表。 简单的一对多的关系，每个学校都附属于一个地区。 我的查询如下：

SELECT schools.id AS schoolid, schools.name AS school, districts.id AS districtid, districts.name AS district FROM sms_schools AS schools LEFT JOIN sms_districts AS districts ON schools.districtid = districts.id WHERE 1 = 1 ORDER BY districts.name, schools.name 

我离开的原因是因为不是每所学校都附属于一个地区。 例如，一所学校可能会在家接受教育，可能包含所有在家接受教育的学生。 那不会在一个地区。

所以我想要做的是使用ORDER BY按照地区名称和学校名称进行sorting。 唯一的问题是，我希望null区位于底部，这样我就可以在输出结尾使用一个名为“Other”的组。

在输出结束时，是否可以用空值升序来进行sorting？

Answer 1

提问后只有1分钟，我find了答案。 在order by clause用例中，使null值比其他任何值都有更高的值：

  ORDER BY (CASE WHEN districts.id IS NULL then 1 ELSE 0 END),districts.name, schools.name; 

Answer 2

你可以使用ISNULL()函数。

从MySQL手册 ：

ISNULL（ expr ）

如果expr为NULL ，则ISNULL()返回1 ，否则返回0 。

例如 ：

 ORDER BY ISNULL(districts.name), districts.name, schools.name 

我喜欢用这个而不是MySQL的CASE选项。 请注意，它不可移植，因为ISNULL()不是标准的SQL，在其他版本的SQL中function不同。

Answer 3

默认情况下会在顶部出现空值，但是您可以使用IsNull来分配默认值，这会将其置于所需的位置。

SELECT schools.id AS schoolid,schools.name AS school, districts.id AS districtid, districts.name AS district FROM sms_schools AS schools LEFT JOIN sms_districts AS districts ON schools.districtid = districts.id WHERE 1 = 1 ORDER BY isnull(districts.name,'1'), schools.name
SELECT schools.id AS schoolid,schools.name AS school, districts.id AS districtid, districts.name AS district FROM sms_schools AS schools LEFT JOIN sms_districts AS districts ON schools.districtid = districts.id WHERE 1 = 1 ORDER BY isnull(districts.name,'1'), schools.name 

Answer 4

 SELECT schools.id AS schoolid, schools.name AS school, districts.id AS districtid, districts.name AS district, if(schools.districtid IS NULL,1,0) as sort FROM sms_schools AS schools LEFT JOIN sms_districts AS districts ON schools.districtid = districts.id WHERE 1 = 1 ORDER BY sort, districts.name, schools.name 

把任何更多的sorting规则insite“新”colunm，并使用任何数字隐藏在您的代码中的字段，testing是否属于如果直接sorting（if by …）

祝你好运