什麼是在給定的查詢

Question

錯誤雖然上午執行查詢

SELECT TIMESTAMPDIFF(SECOND, NOW(), 'select lastLoginTime from requests where id = 2 ') 

它返回NULL。任何想法爲什麼？

Answer 1

mysql> SELECT TIMESTAMPDIFF(SECOND, NOW(), 'select last_update from t1 where actor_id = 2 '); 
+--------------------------------------------------------------------------------+ 
| TIMESTAMPDIFF(SECOND, NOW(), 'select last_update from t1 where actor_id = 2 ') | 
+--------------------------------------------------------------------------------+ 
|                   NULL | 
+--------------------------------------------------------------------------------+ 
1 row in set, 1 warning (0.00 sec) 

刪除「，添加（）

mysql> SELECT TIMESTAMPDIFF(SECOND, NOW(), (select last_update from t1 where actor_id = 2)); 
+-------------------------------------------------------------------------------+ 
| TIMESTAMPDIFF(SECOND, NOW(), (select last_update from t1 where actor_id = 2)) | 
+-------------------------------------------------------------------------------+ 
|                 -199167725 | 
+-------------------------------------------------------------------------------+ 
1 row in set (0.00 sec)