Just wanted to add, any application that wants to store forms data without having to create a new table every time you create a new form could benefit from dynamic columns. 

In the database design world, any design that is of the EAV (Entity-Attribute-Value) style would benefit from dynamic columns.  Having to extract and analyze EAV tables, for the developer, is tricky and burdensome.   This model seems to show up in the literature first in Medical settings and is used in  basic science research as well. (see http://en.wikipedia.org/wiki/Entity%E2%80%93attribute%E2%80%93value_model)

For those that need it, dynamic columns is powerful and makes life much easier.  Unfortunately, often those that need dynamic columns do not know it exists.  If they did, they would jump for joy.

Adam

On Wed, Jan 28, 2015 at 3:41 PM, Oleksandr Byelkin <sanja@montyprogram.com> wrote:

Hi, Tom!

On 28.01.15 23:01, Tom Worster wrote:

While functions for getting and setting via json might be useful, I think they are peripheral to the core datatype problem here.

 The interface to dynamic columns in Maria is SQL. The internal datatypes are SQLish. We can be completely sure of what was set, in SQL terms, by a COLUMN_CREATE(). But if we use a JSON getter then we might get something different because JSON datatypes don't match SQL datatypes. Sometimes it's no problem but not in general -- depends on the datatypes involved and the application's tolerance of differences.

AFAIK we lack only boolean type and arrays (could be emulated now but you can't say if it is array or object with numeric keys) to fit json types.

column_create/alter do not require type (detect automatically), so type there can be mentioned to enforce some encoding you want (store dates as dates but not string)

column_get() require type of output, if you do not care use CHAR. But this is required by SQL expression implementation. There is json output which do not need type of columns.

What's missing is a getter that tells us the value and datatype of a dynamic column, a getter that tells us what was set.

What if we had a getter that returns a string like:

COLUMN_GET_SQL(`product`, 'price')
>> "CAST(123.456 AS DECIMAL(11,3))"

And Maria promises us that we could use that expression to write the value back and the result will be the exact same thing. A sort of idempotency promise (kinda).

This doesn't make the interface any less clunky (on the contrary) but I have resigned myself to a clunky interface. The only alternative is to forget all this and start something different. SQL is an insanely clunky old language and that's why we use some kind of abstraction software to make it nicer. If we're going to use SQL we may as well try to use what's there.

Something like this COLUMN_GET_SQL() would at least allow the application the possibility to get back what it put in.

I am not sure that I understand what you need. Is it ability to know internal storage type?

[skip]

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