问题描述
今天早上我正在学习 MySQL 中的存储过程/函数/触发器,但我在尝试在查询中使用变量表和列名时遇到了一些问题.
I'm learning stored procedures/functions/triggers in MySQL this morning and I'm having some problems trying to use variable table and column names in queries.
DELIMITER |
USE R2R |
DROP FUNCTION IF EXISTS getCategoryName |
CREATE FUNCTION getCategoryName(LMID INT, levelNum INT)
RETURNS VARCHAR(255)
BEGIN
DECLARE levelName VARCHAR(255) DEFAULT makeLevelName(levelNum);
DECLARE levelID INT;
DECLARE levelNameID VARCHAR(255) DEFAULT CONCAT(levelName, 'ID');
DECLARE ret VARCHAR(255);
SELECT @levelNameID INTO levelID FROM LevelMaster WHERE id=LMID;
SELECT description INTO ret FROM @levelName WHERE id=levelID;
RETURN ret;
END;
|
DROP FUNCTION IF EXISTS makeLevelName |
CREATE FUNCTION makeLevelName(levelNum INT)
RETURNS VARCHAR(255)
BEGIN
DECLARE word VARCHAR(255);
DECLARE ret VARCHAR(255);
IF levelNum=2 THEN SET word='Two';
ELSEIF levelNum=3 THEN SET word='Three';
ELSEIF levelNum=4 THEN SET word='Four';
ELSEIF levelNum=5 THEN SET word='Five';
END IF;
SET ret=CONCAT('Level', word);
RETURN ret;
END;
|
SELECT getCategoryName(347, 2) |
这是导致我出现问题的第一个函数 (getCategoryName),我需要用 @ 标记的两个变量作为表/列名称 - 这两行:
It's the first function (getCategoryName) that's causing me the problems, I need the two variables marked with @ to be the table/column names - these two lines:
SELECT @levelNameID INTO levelID FROM LevelMaster WHERE id=LMID;
SELECT description INTO ret FROM @levelName WHERE id=levelID;
如果可能的话,我想将此函数保留为函数而不是过程,但如果这是唯一的方法,我会接受过程的答案.
I want to keep this function as a function rather than a procedure if possible, but would accept answers for a procedure if it's the only way.
感谢您的帮助,
理查德
推荐答案
为此使用用户/全局变量以及 PREPARE &执行:
Use User/Global Vars for this along with PREPARE & EXECUTE:
SET @columnName='myColumn';
SET @tableName='myTable';
SET @whatEver='requiredValue';
SET @query=CONCAT('SELECT ', @columnName, ' FROM ', @tableName, ' WHERE Column=', @whatEver);
PREPARE QUERY FROM @QUERY;
EXECUTE QUERY;
还没有测试过这个 EXACT 代码,但这些代码会起作用.也必须在程序内,不能与函数或触发器一起使用,如果有人有解决方案,请发布.
Haven't tested this EXACT code but something along these lines will work. Also has to be inside a Procedure, cannot be used with a function or trigger, if anyone has a soloution for that then please post.
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