在mysql中的一个选择案例中的情况

Question

我厌倦了尝试连接到MSSQL,所以我转而使用mysql.这是缓慢的进展.这是我目前的傻瓜: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

我想把它切换到mysql.是否有一种有效的mysql方式:

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

这将指导您在MySQL中使用Inline IF和CASE语句

片段:

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

要么

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

mysql> SELECT @val;