On 01/19/19 23:49, Pavel Stehule wrote:
> If I remember, described functionality was implemented in early patches,
> but was removed to simplify code. To now, there was not a request to do it.
>
> Unfortunately, the documentation was not fixed.
I'll do that, as I'm working in there anyway. :)
> column expressions are evaluated once per row, but XPath expression is
> compiled per row too, if I remember well.
I looked for evidence of that in the code, but did not find it; the
compilation appears to happen in XmlTableSetColumnFilter, which is
called from tfuncInitialize.
I can't guarantee I didn't miss something, though.
> We designed it more tolerant as
> we expected possibility to store XPath expression in one column and data in
> second column.
Perhaps if I could see an example showing the functionality... The nearest
I could find in the regression tests was the test with
COLUMNS a int PATH '' || lower(_path) || 'c'
but, again, I think that test only demonstrates how LATERAL works, not
any behavior specific to xmltable.
Regards,
-Chap