来自变量的mysql字段名称

问题描述

是否可以选择名称为字符串的字段?

is it possible to select field which name is string?

SELECT 'fieldname' FROM table

我需要这个触发器才能有动态字段名称类似的东西

i need this for trigger to have dynamic field names something like

SET fieldname = NEW.`name`;
UPDATE table SET fieldname = 1 ; 

推荐答案

如果字符串在您的外部应用程序(如 PHP)中，当然，只需构建 MySQL 语句即可.

If the string is in your external application (like PHP), sure, just construct the MySQL statement.

如果字符串在 MySQL 表中，则不能.MySQL 没有 eval() 或这样的函数.以下是不可能的:

If the string is inside a MySQL table, you can't. MySQL has no eval() or such function. The following is impossible:

假设您有一个表 queries，其字段 columnname 引用了表 mytable 中的列名之一.queries 中可能还有其他列，允许您选择所需的 columnname.

Suppose you have a table queries with a field columnname that refers to one of the column names in the table mytable. There might be additional columns in queries that allow you to select the columnname you want.

INSERT INTO queries  (columname) VALUES ("name")
SELECT (select columnname from queries) from mytable

然而，您可以使用 PREPARED STATEMENTS.请注意，这非常棘手.

You can however work with PREPARED STATEMENTS. Be aware this is very hacky.

SELECT columnname from queries into @colname;
SET @table = 'mytable';
SET @s = CONCAT('SELECT ',@colname,' FROM ', @table);

PREPARE stmt FROM @s;
EXECUTE stmt;

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