DB2 SQL - 在触发器完成后无法成功插入到表中

Question

我在插入触发器后将值插入表中时遇到了问题。 触发器如下：

CREATE TRIGGER trig
AFTER INSERT ON Follows
REFERENCING NEW as N
FOR EACH row
WHEN ((Select email from Celebrity) <> N.followed_email)
UPDATE followSuggestion SET followSuggestion.Suggested_follower = N.followed_email, followSuggestion.Suggested_followee = N.follower_email
;

插入代码如下：

INSERT INTO follows
VALUES('Michael_Phelps@uss.net','Michael_Phelps@uss.net');

错误如下

DB21034E  The command was processed as an SQL statement because it was not a 
valid Command Line Processor command.  During SQL processing it returned:
SQL0811N  The result of a scalar fullselect, SELECT INTO statement, or VALUES 
INTO statement is more than one row.  SQLSTATE=21000

SQL0811N  The result of a scalar fullselect, SELECT INTO statement, or VALUES INTO statement is more than one row.

先谢谢你了！

Answer 1

我认为这是问题所在：

 (Select email from Celebrity) <> N.followed_email

子查询可能会返回多行，因此标量运算符＆lt;＆gt;不管用。 您必须将该条件改为：

WHEN ((Select COUNT(email) from Celebrity WHERE email = N.followed_email) = 0) ...