How Can I Dynamically Retrieve and Use Field Names in MySQL Queries?

Dynamic Field Name Retrieval in MySQL

Question:

Can one dynamically retrieve a field name in MySQL based on a variable?

Background:

In some scenarios, such as when working with triggers, it may be necessary to dynamically update a field whose name is not known beforehand.

Code Sample:

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

Answer:

In MySQL, direct access to field names from variables is not possible. However, there are two methods to address this need:

1. External Construction (if Variable is in External Application):

If the field name is available in an external application, such as PHP, you can construct the MySQL statement dynamically.

Example:

$fieldName = "fieldname";
$sql = "SELECT $fieldName FROM table";

2. Prepared Statements (for Variables Stored in MySQL):

If the field name is stored in a MySQL table, you can use prepared statements to achieve the desired behavior.

Code Sample:

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

PREPARE stmt FROM @s;
EXECUTE stmt;

Note: Prepared statements require careful handling of variable substitution and potential SQL injection vulnerabilities.

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