How Can I Dynamically Select and Update MySQL Fields Using Variables?

Dynamic Field Selection in MySQL Based on a Variable

It is often necessary in database programming to dynamically select fields based on variable values. This can be particularly useful in scenarios where field names are unknown or vary dynamically.

Field Selection Using a String Variable

Question: Is it possible to select a field whose name is stored in a string variable in MySQL?

SELECT 'fieldname' FROM table;

Answer: Yes, it is possible to construct the MySQL statement dynamically using the string variable:

SET @fieldname = 'name';
SELECT @fieldname FROM table;

Dynamic Updates Using Field Variables

Question: How can I perform updates on a table using a variable that represents the field name in MySQL?

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

Answer: It is not possible to use an arbitrary string as a field name in MySQL directly. However, you can employ a workaround using MySQL's PREPARED STATEMENTS feature:

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

PREPARE stmt FROM @s;
EXECUTE stmt;

This allows you to create a prepared statement with a dynamic field name based on the value stored in the variable @colname.

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