无法使用该表上的条件调用更新表

Question

我尝试通过调用该表上的条件来更新表，并得到错误消息。

update grade G
set G.`score` = G.`score` + 5
where G.`snum` IN (select G1.`snum` from grade G1 where G1.`cname` ='Database Systems' And G1.`score` <> 'NULL' AND G1.`score` <= 95));

我不知道为什么会给我语法错误 因为这条波纹管给了我2个满足条件的编号。

where G.`snum` IN (select G1.`snum` from grade G1 where G1.`cname` ='Database Systems' And G1.`score` <> 'NULL' AND G1.`score` <= 95));

Answer 1

如果是同一张表，则不需要子查询，只需将条件直接添加到where子句中即可：

update grade G
   set G.`score` = G.`score` + 5
 where G.`cname` ='Database Systems' 
   And G.`score` <> 'NULL'
   AND G.`score` <= 95;

这里的And G.score <> 'NULL'应该是G.score is not null。除非您将null作为字符串

Answer 2

最后有2个右括号，请删除1个括号