Re: CREATE TABLE creates a composite type corresponding to the table row, which is and is not there

On Thu, Apr 4, 2024 at 12:41 AM Erik Wienhold <ewie(at)ewie(dot)name> wrote:
> Thanks, fixed in v4. Looks like American English prefers that comma and
> it's also more common in our docs.

Reviewing this patch:

- Creates a <firstterm>typed table</firstterm>, which takes its
- structure from the specified composite type (name optionally
- schema-qualified). A typed table is tied to its type; for
- example the table will be dropped if the type is dropped
- (with <literal>DROP TYPE ... CASCADE</literal>).
+ Creates a <firstterm>typed table</firstterm>, which takes its structure
+ from an existing (name optionally schema-qualified) stand-alone composite
+ type (i.e., created using <xref linkend="sql-createtype"/>) though it
+ still produces a new composite type as well. The table will have
+ a dependency on the referenced type such that cascaded alter and drop
+ actions on the type will propagate to the table.

It would be better if this diff didn't reflow the unchanged portions
of the paragraph.

I agree that it's a good idea to mention that the table must have been
created using CREATE TYPE .. AS here, but I disagree with the rest of
the rewording in this hunk. I think we could just add "creating using
CREATE TYPE" to the end of the first sentence, with an xref, and leave
the rest as it is. I don't see a reason to mention that the typed
table also spawns a rowtype; that's just standard CREATE TABLE
behavior and not really relevant here. And I don't understand what the
rest of the rewording does for us.

<para>
- When a typed table is created, then the data types of the
- columns are determined by the underlying composite type and are
- not specified by the <literal>CREATE TABLE</literal> command.
+ A typed table always has the same column names and data types as the
+ type it is derived from, and you cannot specify additional columns.
But the <literal>CREATE TABLE</literal> command can add defaults
- and constraints to the table and can specify storage parameters.
+ and constraints to the table, as well as specify storage parameters.
</para>

I don't see how this is better.

- errmsg("type %s is not a composite type",
+ errmsg("type %s is not a stand-alone composite type",

I agree with Peter's complaint that people aren't going to understand
what a stand-alone composite type means when they see the revised
error message; to really help people, we're going to need to do better
than this, I think.

--
Robert Haas
EDB: http://www.enterprisedb.com