How would you create and store user-defined custom fields in a SQL database?

Question

I need to allow users to add new fields to a record, e.g. if there is a Contact record, a user may want to add a \"SSN\" numeric field and a \"Birthdate\" date/calendar fiel

Answer 1

Have a table that stores the field names and types.

field_ID     INT
field_name   VARCHAR
field_type   ENUM('int','float','text','richtext')

Have a table that stores a link to an entry in the record table, a link to an entry in the field table, and the field value.

fieldvalue_fieldID   INT
fieldvalue_recordID  INT
fieldvalue_value     BLOB

Making it searchable is another challenge - you would need to grab any searchable content out of that fieldvalue_value and index that. This would be database-specific. In MySQL you could make that a TEXT value and add a MySQL FULLTEXT index on it.