mysql - 中间函数/查询奇数和偶数字符串

Question

我需要一个查询，它给出偶数字符串的两个中间字符和奇数字符串的一个中间字符。

目前我正在使用此代码，但它给出了错误。

SELECT S_name, MID(S_name, LENGTH(S_name)/2,1) WHERE (LENGTH(S_name) %2) = 1 OR/AND SELECT S_Name, MID(S_name,LENGTH(S_name)/2,2) WHERE (LENGTH(S_name)%2)=0 FROM Student;

我也尝试过此代码，但它返回空 View /表。

SELECT S_name FROM Student WHERE ((LENGTH(S_name) %2) = 1 AND SUBSTRING(S_name, LENGTH(S_name)/2+1, 1)) OR ((LENGTH(S_name) %2) = 0 AND SUBSTRING(S_name, LENGTH(S_name)/2-1, 2)) 

请看一下并指出我的错误。

Answer 1

您想在 select 子句中使用 case:

select s_name,
       (case when length(s_name) % 2 = 0 then substring(s_name, length(s_name)/2, 2)
             else substring(s_name, 1 + length(s_name) / 2, 1)
        end)
from student;