sql - DB2 SQL - 触发后无法成功插入表

Question

在附加了触发器后，我在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.

提前谢谢你！

Answer 1

我认为这是问题所在：

 (Select email from Celebrity) <> N.followed_email

子查询可能会返回不止一行，因此标量运算符 <> 将不起作用。您将不得不将该条件改写为：

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