第一次發生other_field = value時更新字段？

Question

Here's the following SQL in SQL Fiddle.

+-----+-----+-------------+ 
| id | rel | content  | 
+-----+-----+-------------+ 
| 1 | 1 | example 1 | 
| 2 | 2 | test 2 oops | 
| 3 | 1 | example 2 | 
| 4 | 2 | test 2  | 
+-----+-----+-------------+ 

如何申請SET content = "test 1"到僅在第一記錄WHERE rel = 2 ORDER BY id ASC不知道該記錄的ID？沒有任何子查詢可以這樣做嗎？

Answer 1

假設「第一」意味着第一行的結果時，由id下令：

update example set content = 'test 1' where rel = 2 order by id limit 1;