On Fri, 30 Aug 2013 16:28:37 +0200, "Robbert-Jan"
<rjm_eabonnem...@xs4all.nl> wrote:
> Hi,
>
> I like to propose a more consistent syntax for computed columns and
> identity columns:
>
> Computed columns are now defined in DDL as
>
> <ColumnName> [<DataType>] GENERATED ALWAYS AS (<Expression>)
>
> while identity columns (as of FB 3.0 CORE-1385) are defined as:
>
> <ColumnName> {<DataType>|<DomainName>} GENERATED {ALWAYS|BY DEFAULT} AS
> IDENITITY
>
> Note the differences:
> - for computed columns the datatype is optional (if ommitted the system
> will find an appropriate datatype)
> - identity columns can be defined as both datatype and domain, where
> computed columns can only be defined as datatype
> - identity columns can be defined as both ALWAYS (although not yet
> implemented) and BY DEFAULT, while computed columns can only be defined
as
> ALWAYS
>
> To make this more consistent, I like to propose to:
> - also support domains for computed columns;
> - also make the specification of datatype/domain for identity columns
> optional (if it is ommitted the system should assume INTEGER);
> - also support GENERATED BY DEFAULT for computed columns.
>
>
> The syntax will then also be more generic (covering both computed and
> identity columns):
>
> generated column specification ::= <ColumnName>
> [{<DataType>|<DomainName>}] GENERATED {ALWAYS|BY DEFAULT} AS
> {(<Expression>)|IDENTITY}
I am not entirely sure what the SQL Specification says as I don't have it
handy right now, but the current syntax is derived from the specification.
I also am not sure if a GENERATED BY DEFAULT AS ... makes sense for a
computed column, as it would imply it is a normal column that has a default
(which already has a separate clause) and not a computed one.
Mark
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