我在 MYSQL 中使用 IF 语句有一个特殊的问题。我有一个存储函数，它将表的内容作为字符串返回。为了让我的字符串返回正确数量的结果，我准备了一个基于数字的选择语句。如果数字是 <= 9，那么一个 sql 语句和 9 个以上的另一个。
但是，在序列中，我只能将 if 语句放在函数的末尾。如果我把它放在正确的位置，它当前被注释掉，它会给我一个语法错误。如果我将 if 语句放在函数的末尾不正确的地方，我不会收到错误。
请帮忙。我不知道这是一个错误还是我自己的错误。
DELIMITER $$
CREATE DEFINER=`root`@`localhost` FUNCTION `returnstring`(IDGrade int) RETURNS varchar(255) CHARSET latin1
BEGIN
Declare fSubjectID, sSubjectID varchar (255);
declare sqlstatement varchar(255);
#Declare variable for done of loop
Declare done int default 0;
#Declare variables from the select statement
#IF IDGRADE <= 9 then set sqlstatement = 'SELECT subjectID FROM subjecttb where sectType = "b" or secttype = "j" order by subjectID';
#ELSEIF IDGRADE > 9 then set sqlstatement = 'SELECT subjectID FROM subjecttb where sectType = "b" or secttype = "s" order by subjectID';
#END IF;
#Declare a cursor to iterate through the table
declare cursor1 cursor for
SELECT subjectID
FROM `marksdb`.`subjecttb`
where sectType = 'b' or secttype = 'j' order by subjectID;
#Continue loop until nothing is found anymore
declare continue handler for not found set done=1;
#Runs the select statement
open cursor1;
#Declares a loop
set fsubjectid='';
SubjectID_loop:loop
Fetch cursor1 into sSubjectID;
if done=1 then # no more rows to fetch
leave SubjectID_loop;
end if;
set fSubjectID = concat(fSubjectID, sSubjectID , ' varchar (255), ');
end loop SubjectID_loop;
set fSubjectID = substring(fSubjectID, 1, length(fsubjectid)-2);
close cursor1;
return fSubjectID;
#Declare variables from the select statement
IF IDGRADE <= 9 then set sqlstatement = 'SELECT subjectID FROM subjecttb where sectType = "b" or secttype = "j" order by subjectID';
ELSEIF IDGRADE > 9 then set sqlstatement = 'SELECT subjectID FROM subjecttb where sectType = "b" or secttype = "s" order by subjectID';
END IF;
结尾