Вы, вероятно, хотите по крайней мере три таблицы:
CREATE TABLE form_fields (
id INT NOT NULL AUTO_INCREMENT,
form_name VARCHAR(50),
field_name VARCHAR(20),
PRIMARY KEY (`id`),
UNIQUE KEY `real_pk` (`formname`,`fieldname`)
);
CREATE TABLE forms_completed (
id INT NOT NULL AUTO_INCREMENT,
form_name VARCHAR(20),
... other info about this instance of the form,
e.g. submitted date, submitted by...
PRIMARY KEY (`id`),
FOREIGN KEY (form_name) REFERENCES form_fields(form_name)
ON DELETE CASCADE
);
CREATE TABLE form_values (
id INT NOT NULL AUTO_INCREMENT,
form_instance IN NOT NULL,
form_name VARCHAR(50), /* only required to force referential integrity */
field_name VARCHAR(20),
date_value DATETIME,
int_value INT,
float_value FLOAT,
string_value VARCHAR(100),
PRIMARY KEY (`id`),
FOREIGN KEY (form_instance) REFERENCES forms_completed(id)
ON DELETE CASCADE,
FOREIGN KEY (form_name, field_name)
REFERENCES form_fields(form_name, field_name)
ON DELETE CASCADE
);