mysql 查询某个字段并拼接case when出来的字段

Posted 2023-05-16

sql语句如下：
select
stf.stationName+'('+(case stf.stationType when 'RAIN' then '雨情站'
when 'REGIMEN' then '水位站'
else '流量站' end
)+')' AS text

from radar_stations_info stf
想得到的结果是 长沙（雨情站）或者 长沙（水位站）或者 长沙（流量站）
为什么同样的语句可以再sqlserver中运行在oracle中运行就是不能在mysql中运行呢？

参考技术A select case stf.stationType when 'RAIN' then '雨情站' when 'RECIMEI' then '水位站' else '流量站' end tationName from radar_stations_info stf追问

已经做出来了，谢谢您的回答

mysql根据某个字段排序，order by case when使用

解决了遇到的问题，转载记录一下；
本篇文章为大家展示了MySQL中怎么按照指定的字段排序，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

用到的测试数据

drop table a;

create table a (x varchar(10),y varchar(10));

insert into a values('yujx','all'),('oracle','pc'),('mysql','mobile');

#表a的测试数据如下

MySQL>select * from a;
+--------+--------+
| x      | y      |
+--------+--------+
| yujx   | all    |
| oracle | pc     |
| mysql  | mobile |
+--------+--------+
3 rows in set (0.00 sec)

#默认的按y排序（升序或降序）结果

MySQL>select * from a order by y;
+--------+--------+
| x      | y      |
+--------+--------+
| yujx   | all    |
| mysql  | mobile |
| oracle | pc     |
+--------+--------+
3 rows in set (0.00 sec)

MySQL>select * from a order by y desc;
+--------+--------+
| x      | y      |
+--------+--------+
| oracle | pc     |
| mysql  | mobile |
| yujx   | all    |
+--------+--------+
3 rows in set (0.00 sec)

现在想按mobile->all->pc的顺序排序，可使用如下方法
方法一：使用 FIND_IN_SET(str,strlist) 函数

MySQL>select * from a order by find_in_set(y,'mobile,all,pc');
+--------+--------+
| x      | y      |
+--------+--------+
| mysql  | mobile |
| yujx   | all    |
| oracle | pc     |
+--------+--------+
3 rows in set (0.00 sec) 

方法二：使用FIELD(str,str1,str2,str3,…)函数
#FIELD函数主要用途会返回值在后面列表中的位置，如下

MySQL>select x,y,field(y,'mobile','pc','all') sort_Nu from a order by field(y,'mobile','pc','all');   
+--------+--------+---------+
| x      | y      | sort_Nu |
+--------+--------+---------+
| mysql  | mobile |       1 |
| oracle | pc     |       2 |
| yujx   | all    |       3 |
+--------+--------+---------+
3 rows in set (0.00 sec)

方法三：使用 SUBSTRING_INDEX(str,delim,count) 函数

MySQL>select * from a order by substring_index('mobile,all,pc',y,1);
+--------+--------+
| x      | y      |
+--------+--------+
| mysql  | mobile |
| yujx   | all    |
| oracle | pc     |
+--------+--------+
3 rows in set (0.00 sec)

#看下面 substring_index(‘mobile,all,pc’,y,1) 取值,可知按b列的值排序 y的顺序固然就是 mobile,all,pc了

MySQL>select y,substring_index('mobile,all,pc',y,1) b  from a;
+--------+-------------+
| y      | b           |
+--------+-------------+
| all    | mobile,     |
| pc     | mobile,all, |
| mobile |             |
+--------+-------------+
3 rows in set (0.00 sec)

方法四：使用case when

MySQL>select x,y,case when y='mobile' then 1 when y='all' then 2 when y='pc' then 3 end sort_nu from a order by  case when y='mobile' then 1 when y='all' then 2 when y='pc' then 3 end;

+--------+--------+---------+
| x      | y      | sort_nu |
+--------+--------+---------+
| mysql  | mobile |       1 |
| yujx   | all    |       2 |
| oracle | pc     |       3 |
+--------+--------+---------+
3 rows in set (0.00 sec)

转载自：MySQL中怎么按照指定字段排序