mysql - mysql中选择案例中的案例

Question

我已经厌倦了尝试连接到 MSSQL，所以我要切换到 mysql。 进展缓慢。这是我目前的障碍: 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

我想将其切换到 mysql。是否有有效的 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

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;