mysql case 问题

[zxcjqyy]

case 字段名 when 和 case when 有什么区别

[Semoz]

CASE type WHEN 1 THEN 'a' WHEN 2 THEN 'b' ELSE 'c' END

CASE WHEN type > 5 THEN 'd' WHEN type < 0 THEN 'e' ELSE 'f' END

你说啥区别？

[zxcjqyy]

SELECT (CASE
WHEN MOD(id,2) = 1 AND id = (SELECT COUNT(*) FROM seat) THEN id
WHEN MOD(id,2) = 1 THEN id+1
ElSE id-1
END) AS id, student
FROM seat
ORDER BY id;


select (case id when mod(id,2)=1 and id = (select count(*) from seat) then id
when mod(id,2)=1 then id+1
else id-1
end)id, student
from seat
order by id

那这 2 个 sql 结果为什么会不一样