WHERE CURRENT OF 有什么作用

来源：学生作业帮编辑：作业帮分类：综合作业时间：2024/11/08 11:13:32

WHERE CURRENT OF 有什么作用
Select For Update有什么作用

如果你想删除或者更新被Select For Update引用的记录,你可以使用Where Current Of语句.
UPDATE table_name
SET set_clause
WHERE CURRENT OF cursor_name;
OR
DELETE FROM table_name
WHERE CURRENT OF cursor_name;
Where Current Of语句允许你更新或者是删除最后由cursor取的记录.
下面一个使用Where Current Of更新记录的例子：
CREATE OR REPLACE Function FindCourse
( name_in IN varchar2 )
RETURN number
IS
cnumber number;
CURSOR c1
IS
SELECT course_number,instructor
from courses_tbl
where course_name = name_in
FOR UPDATE of instructor;
BEGIN
open c1;
fetch c1 into cnumber;
if c1%notfound then
cnumber := 9999;
else
UPDATE courses_tbl
SET instructor = 'SMITH'
WHERE CURRENT OF c1;
COMMIT;
end if;
close c1;
RETURN cnumber;
END;
Deleting using the WHERE CURRENT OF Statement
Here is an example where we are deleting records using the Where Current Of Statement:
译：下面一个使用Where Current Of删除记录的例子：
CREATE OR REPLACE Function FindCourse
( name_in IN varchar2 )
RETURN number
IS
cnumber number;
CURSOR c1
IS
SELECT course_number,instructor
from courses_tbl
where course_name = name_in
FOR UPDATE of instructor;
BEGIN
open c1;
fetch c1 into cnumber;
if c1%notfound then
cnumber := 9999;
else
DELETE FROM courses_tbl
WHERE CURRENT OF c1;
COMMIT;
end if;
close c1;
RETURN cnumber;
END;

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