MySQL mysql中选择案例中的案例
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case within a select case in mysql
提问by Charles McAnany
I'm getting sick of trying to hook up to MSSQL, so I'm switching over to mysql. It's slow progress. Here's my current stumper: mssql:
我厌倦了尝试连接到 MSSQL，所以我切换到 mysql。这是缓慢的进展。这是我目前的绊脚石：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
I'd like to switch this to mysql. Is there a valid mysql way to:
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
? How about
? 怎么样
set var = select case n when [...] end
?
?
回答by John Woo
this will guide you in using Inline IF and CASE statements in MySQL
这将指导您在 MySQL中使用内联 IF 和 CASE 语句
snippet:
片段：
SELECT CASE num_heads
WHEN 0 THEN 'Zombie'
WHEN 1 THEN 'Human'
ELSE 'Alien'
END AS race
FROM user
or
或者
mysql> SET @val := CASE num_heads
WHEN 0 THEN 'Zombie'
WHEN 1 THEN 'Human'
ELSE 'Alien'
END AS race;
mysql> SELECT @val;
回答by ruakh
Do you mean
你的意思是
SET @var := CASE n WHEN [...] END;
?
?
(http://dev.mysql.com/doc/refman/5.6/en/user-variables.html)
( http://dev.mysql.com/doc/refman/5.6/en/user-variables.html)
