Question

我试图解决的问题：

返回＆＃34;前缀＆＃34;的值遵循以下条件：

如果model_hyouji是一个数字，范围从0到9，请设置prefix = 0
如果model_hyouji是一个字母，范围从a到z或A到Z，请设置prefix = 1
在所有其他情况下，请设置prefix = 2

我使用了这个SQL：

SELECT model_code,
       model_hyouji,
       model_name_prefix,
       model_kana_prefix,
       model_count,
       case prefix
            when 'a' then 1
            when 'b' then 2
            else 3
       end
FROM    webikept.mst_model_v2 
where   model_maker_code = 1 
and     model_displacement between 51 and 125 
and     (SELECT substring(model_hyouji,1,1) as prefix
        FROM webikept.mst_model_v2 )

我收到此错误：

未知栏＆＃39; prefix＆＃39;在＆＃39; field list＆＃39;

Answer 1

假设你的列model_hyouji是varchar（1）（否则使用substr（model_hyouji，1））

  SELECT model_code,
         model_hyouji,
         model_name_prefix,
         model_kana_prefix,
         model_count,
         case 
              when  model_hyouji between '0' and '9' then 0 
              when  model_hyouji between 'a' and 'z' then 1 
              when  model_hyouji between 'A' and 'Z' then 1 
              else 2 
          end prefix
  FROM    webikept.mst_model_v2 
  where   model_maker_code = 1 
  and     model_displacement between 51 and 125 
  and     (SELECT substring(model_hyouji,1,1) as prefix
          FROM webikept.mst_model_v2 )

或者您可以使用regexp

  SELECT model_code,
         model_hyouji,
         model_name_prefix,
         model_kana_prefix,
         model_count,
         case 
              when  model_hyouji REGEXP  '^[0-9]{1}$' then 0 
              when  model_hyouji  REGEXP  '^[A-Za-z]$' then 1 
              else 2 
          end prefix
  FROM    webikept.mst_model_v2 
  where   model_maker_code = 1 
  and     model_displacement between 51 and 125 
  and     (SELECT substring(model_hyouji,1,1) as prefix
          FROM webikept.mst_model_v2 )

Answer 2

    SELECT 

  model_code,model_hyouji,model_name_prefix,model_kana_prefix,model_count,
  case 
  when prefix = 'a' then 1 when 'b' then 2 else 3 end

前缀=

时需要CASE

但您也没有指定要使用的前缀列，因此未知列上的错误

E.G

  SELECT 

  model_code,model_hyouji,model_name_prefix,model_kana_prefix,model_count,
  case 
  WHEN model_kana_prefix = 'a' then 1 
  WHEN model_kana_prefix = 'b' then 2 
  else 3 end

在Mysql中使用select case

2 个答案: