变量中的mysql字段名称 [英] mysql field name from variable

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

我需要使用它来使触发器具有动态字段名称 像

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

如果该字符串在您的外部应用程序(如PHP)中，请确保构造MySQL语句.

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()或此类功能.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，其中的字段columnname引用了表mytable中的列名之一. queries中可能还有其他列，可让您选择所需的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

但是，您可以使用 PREPARED STATEMENTS .请注意，这很hacky.

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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