例如，代码“起作用”

drop table if exists event;
create table event(event_id int, event_type varchar(1), event_title varchar(10));

insert into event values
(1,'c','aaa'),(2,'x','xxx');

select event_id,
       IF(event_type!='C',e.event_title ,'') event_title,
       IF(event_type='C', e.event_title ,'') event_subtitle
from event e;

+----------+-------------+----------------+
| event_id | event_title | event_subtitle |
+----------+-------------+----------------+
|        1 |             | aaa            |
|        2 | xxx         |                |
+----------+-------------+----------------+
2 rows in set (0.00 sec)

如果您的数据模型不是这样的，或者基于我的示例数据的输出不是您所期望的，请将示例数据和所需的输出作为文本添加到问题中。

检查此项：

select event_id,
       case when event_type<>'C' then e.event_title  end  as  event_title,
       case when event_type='C'then e.event_title end as  event_subtitle
from event where log_id='%s';

例如：

SELECT ename ,
case when job='SALESMAN' then  ename end as  salesman_ename,
case when job<>'SALESMAN' then  ename end as not_salesman_ename
FROM scott.emp;

SMITH       SMITH
ALLEN   ALLEN   
WARD    WARD    
JONES       JONES
MARTIN  MARTIN  
BLAKE       BLAKE
CLARK       CLARK
SCOTT       SCOTT
KING        KING
TURNER  TURNER  
ADAMS       ADAMS
JAMES       JAMES
FORD        FORD
MILLER      MILLER
H       H

我想知道你是否需要：

select event_id,
       max(case when event_type <> 'C' then e.event_title end) as event_title,
       max(case when event_type = 'C' then e.event_title end) as event_subtitle
from event e
where log_id = '%s'
group by event_id;

你在写什么 event_title 在这两种情况下，但根据你的要求，我知道你想要 IF(event_type='C', e.event_subtitle ,'') event_subtitle 更改自

IF(event_type!='C',e.event_title ,'') event_title,
IF(event_type='C', e.event_title ,'') event_subtitle

到

IF(event_type!='C',e.event_title ,'') event_title,
IF(event_type='C', e.event_subtitle ,'') event_subtitle
                      ^^^^^^^^^^^