MySql 在 SELECT 语句中使用 CASE 时的多重输出

Question

用case时，结果中怎么取出两个东西？

例如:

set @x = 1;

select case when UserId = @x 
then
concat('Test'), // This is the part I fail at. It'll output either one, but not more.
userName 
end from my_members;

Answer 1

您需要两个 case 语句:

set @x = 1;

select (case when UserId = @x then concat('Test') end) as col1
       (case when UserId = @x then userName end) as userName
from my_members;

就个人而言，我确实希望 case 语句允许多列返回，但这需要对 SQL 进行大量更改。