mysql中select case中的case

Question

我厌倦了尝试连接到MSSQL，所以我切换到mysql。进展很慢。这是我目前的难题: mssql：

create function W(m varchar(255)) returns int begin

declare @e int
set @e = (select COUNT(N) from P where N = m)

declare @t int
set @t = dbo.C(m)

return case @t 
when 0 then -1 
when 1 then
    case @e when 0 then -1 else 1 end
when 2 then
    case @e when 1 then -1 when 2 then 0 when 3 then 0 when 4 then 1 end
when 3 then 
    case @e when 1 then -1 when 2 then 1 end
when 4 then 
    case @e when 1 then -1 when 2 then 0 when 3 then 1 end
end
end

我想把这个换成mysql。有没有一种有效的mysql方法：

select select case n when 0 then 1 when 1 then 2 end into var

？怎么样

set var = select case n when [...] end

Answer 1

这将指导您使用Inline IF and CASE statements in MySQL

代码片段：

SELECT CASE num_heads
           WHEN 0 THEN 'Zombie'
           WHEN 1 THEN 'Human'
           ELSE 'Alien'
       END AS race
FROM user

或

mysql> SET @val := CASE num_heads
                       WHEN 0 THEN 'Zombie'
                       WHEN 1 THEN 'Human'
                       ELSE 'Alien'
                   END AS race;

mysql> SELECT @val;

Answer 2

你的意思是

SET @var := CASE n WHEN [...] END;

(http://dev.mysql.com/doc/refman/5.6/en/user-variables.html)