如何在 Oracle 中实现触发器
How in implement Triggers in Oracle
使用 Oracle 11g,我试图通过触发器获取课程名称的最后一个字符,然后根据最后一个字符为学生分配成绩。
我尝试了几种不同的方法来解决这个问题,我得到了几个不同的错误,这让我很头疼。我不确定是我接近光标错误还是整个问题。
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234501,153, '078',256877 , 'Intro to Holographic',"") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234519,153, '078',256877 ,'Intro to Holographic' ,"") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME ,GRADE) VALUES (234505,153, '078',256877 ,'Intro to Holographic', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (23405,21, '012A',23532 ,'Starfleet Intro', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (23419,21, '012A',23532 ,'Starfleet Intro', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (23401,21, '012A',23532 ,'Starfleet Intro', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (23418,21, '012A',23532 ,'Starfleet Intro', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234520,933,'278',843234 ,'Borg Technolgy', "");
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234505,933,'278',843234 ,'Borg Technolgy' ,"");
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234501,933,'278',843234 ,'Borg Technolgy' ,"");
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID, COURSENAME,GRADE) VALUES (234519,438,'531',542303 , 'Intro to Genetics',"");
create or replace TRIGGER gradeTrigger
AFTER Update ON Grade For Each Row
declare
cursor courseTitle_cur IS
select g.COURSENAME
from Grade g;
lastChar String (1);
gradeLetter String(1);
BEGIN
for courseTitle_cur in CourseName
loop
SubStr(CourseName, -1):= lastChar;
end loop;
If(lastChar = 'A' OR lastChar ='B'OR lastChar = 'C' OR lastChar = 'D' OR lastChar = 'E'OR lastChar = 'F') THEN
gradeLetter := "A";
ELSIF(lastChar = 'G'OR lastChar = 'H'OR lastChar = 'I'OR lastChar = 'J'OR lastChar = 'K')THEN
gradeLetter := "B";
ELSIF (LASTCHAR = 'L'or LASTCHAR = 'M'or LASTCHAR = 'N'or LASTCHAR = 'O'or LASTCHAR = 'P')then
gradeLetter := "C";
ELSIf (LASTCHAR = 'Q' OR LASTCHAR = 'R'OR LASTCHAR = 'S'OR LASTCHAR = 'T')THEN
gradeLetter := "D";
ELSIf (lastChar = 'U' OR lastChar ='V'OR lastChar = 'W'OR lastChar = 'X'OR lastChar = 'Y' OR lastChar = 'Z')THEN
gradeLetter := "E";
Return gradeLetter;
end if ;
End;
我收到类似 'Error(16,2): PL/SQL: Statement ignored' 或 'Error(4,10): PL/SQL: ORA-00904: "G"."COURSENAME": invalid identifier' 的错误,这非常令人沮丧,因为我无法查明为什么它被忽略或无效。
我认为您误解了触发器在 Oracle 中的工作方式。
更新的每一行都有前后状态 - 这些分别由 :old
和 :new
记录表示。
如果您想指定应用更新后某个字段的值应该是什么样子,您需要在 之前更改 :new
记录中的字段已应用更新。
因此,我认为您的触发器应该类似于:
CREATE OR REPLACE TRIGGER grade_trigger
BEFORE INSERT OR UPDATE ON grades
FOR EACH ROW
BEGIN
IF substr(upper(:new.coursename), -1) IN ('A', 'B', 'C', 'D', 'E', 'F')
THEN
:new.grade := 'A';
ELSIF substr(upper(:new.coursename), -1) IN ('G', 'H', 'I', 'J', 'K')
THEN
:new.grade := 'B';
ELSIF substr(upper(:new.coursename), -1) IN ('L', 'M', 'N', 'O', 'P')
THEN
:new.grade := 'C';
ELSIF substr(upper(:new.coursename), -1) IN ('Q', 'R', 'S', 'T')
THEN
:new.grade := 'D';
ELSIF substr(upper(:new.coursename), -1) IN ('U', 'V', 'W', 'X', 'Y', 'Z')
THEN
:new.grade := 'E';
END IF;
END grade_trigger;
/
这里是 proof that it works。
使用 Oracle 11g,我试图通过触发器获取课程名称的最后一个字符,然后根据最后一个字符为学生分配成绩。
我尝试了几种不同的方法来解决这个问题,我得到了几个不同的错误,这让我很头疼。我不确定是我接近光标错误还是整个问题。
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234501,153, '078',256877 , 'Intro to Holographic',"") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234519,153, '078',256877 ,'Intro to Holographic' ,"") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME ,GRADE) VALUES (234505,153, '078',256877 ,'Intro to Holographic', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (23405,21, '012A',23532 ,'Starfleet Intro', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (23419,21, '012A',23532 ,'Starfleet Intro', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (23401,21, '012A',23532 ,'Starfleet Intro', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (23418,21, '012A',23532 ,'Starfleet Intro', "") ;
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234520,933,'278',843234 ,'Borg Technolgy', "");
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234505,933,'278',843234 ,'Borg Technolgy' ,"");
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID,COURSENAME, GRADE) VALUES (234501,933,'278',843234 ,'Borg Technolgy' ,"");
INSERT INTO GRADES (STUDNETID, SECTIONID, SECTIONINFO, COURSEID, COURSENAME,GRADE) VALUES (234519,438,'531',542303 , 'Intro to Genetics',"");
create or replace TRIGGER gradeTrigger
AFTER Update ON Grade For Each Row
declare
cursor courseTitle_cur IS
select g.COURSENAME
from Grade g;
lastChar String (1);
gradeLetter String(1);
BEGIN
for courseTitle_cur in CourseName
loop
SubStr(CourseName, -1):= lastChar;
end loop;
If(lastChar = 'A' OR lastChar ='B'OR lastChar = 'C' OR lastChar = 'D' OR lastChar = 'E'OR lastChar = 'F') THEN
gradeLetter := "A";
ELSIF(lastChar = 'G'OR lastChar = 'H'OR lastChar = 'I'OR lastChar = 'J'OR lastChar = 'K')THEN
gradeLetter := "B";
ELSIF (LASTCHAR = 'L'or LASTCHAR = 'M'or LASTCHAR = 'N'or LASTCHAR = 'O'or LASTCHAR = 'P')then
gradeLetter := "C";
ELSIf (LASTCHAR = 'Q' OR LASTCHAR = 'R'OR LASTCHAR = 'S'OR LASTCHAR = 'T')THEN
gradeLetter := "D";
ELSIf (lastChar = 'U' OR lastChar ='V'OR lastChar = 'W'OR lastChar = 'X'OR lastChar = 'Y' OR lastChar = 'Z')THEN
gradeLetter := "E";
Return gradeLetter;
end if ;
End;
我收到类似 'Error(16,2): PL/SQL: Statement ignored' 或 'Error(4,10): PL/SQL: ORA-00904: "G"."COURSENAME": invalid identifier' 的错误,这非常令人沮丧,因为我无法查明为什么它被忽略或无效。
我认为您误解了触发器在 Oracle 中的工作方式。
更新的每一行都有前后状态 - 这些分别由 :old
和 :new
记录表示。
如果您想指定应用更新后某个字段的值应该是什么样子,您需要在 之前更改 :new
记录中的字段已应用更新。
因此,我认为您的触发器应该类似于:
CREATE OR REPLACE TRIGGER grade_trigger
BEFORE INSERT OR UPDATE ON grades
FOR EACH ROW
BEGIN
IF substr(upper(:new.coursename), -1) IN ('A', 'B', 'C', 'D', 'E', 'F')
THEN
:new.grade := 'A';
ELSIF substr(upper(:new.coursename), -1) IN ('G', 'H', 'I', 'J', 'K')
THEN
:new.grade := 'B';
ELSIF substr(upper(:new.coursename), -1) IN ('L', 'M', 'N', 'O', 'P')
THEN
:new.grade := 'C';
ELSIF substr(upper(:new.coursename), -1) IN ('Q', 'R', 'S', 'T')
THEN
:new.grade := 'D';
ELSIF substr(upper(:new.coursename), -1) IN ('U', 'V', 'W', 'X', 'Y', 'Z')
THEN
:new.grade := 'E';
END IF;
END grade_trigger;
/
这里是 proof that it works。