mysql - 错误 1109 (42S02) : Unknown table 'comment' in field list

Question

我使用 MySQL 5.5。我有一个表格 comment。当我进行此查询时:

 select sum(case when comment.entity_id=1 and comment.entity_type=1 then 1 else 0 end) as result1;

我明白了

ERROR 1109 (42S02): Unknown table 'comment' in field list

这不应该发生，因为

select * from comment;

工作得很好。

哪里出错了？

Answer 1

您缺少 FROM 子句:

SELECT SUM(CASE WHEN entity_id = 1 AND entity_type = 1 THEN 1 ELSE 0 END) AS result1
FROM comment