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Asked: 2026-05-15T03:00:01+00:00

I want to add dynamic columns in a mysql table but I don’t know

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I want to add dynamic columns in a mysql table but I don’t know exactly how.

I want to let the user add some columns (fields) in a thread, eg. let him add a integer field and a value (eg. price: 199) or a string field and a value (eg. name: teddybear).

The user can add as many field/value-pairs as he wants.

I thought I could create a many-to-many table:

thread <-> thread_field <-> field

thread: id, title
thread_field: field_id, thread_id, value
field: id, name

is this a good structure?

But in this way I have to set a specific column type of thread_field.value. either it’s an integer or a string. I want to have the possibility to have it dynamic, let the user choose.

How can I do this?

Thanks!

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1 Answer

  1. Editorial Team

    This problem comes up very frequently with regards to relational databases. It’s part of the definition of a relation that it has a fixed set of attributes, not dynamic attributes.

    If you need to allow user-defined attributes in a relational database, the simplest solution is to store a Serialized BLOB such as XML or other semi-structured format (JSON, YAML). You lose the ability to query this efficiently using SQL (unless you use an RDBMS that extends SQL with XML functions and indexes), but you’re going to sacrifice many features of the RDBMS no matter how you solve this problem.

    Another alternative is to use one of the new non-relational data stores like CouchDB or MongoDB, which makes it easy to extend entities with dynamic, strucutred attributes while remaining somewhat efficient.

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