Re: COPY Transform support - Mailing list pgsql-hackers
| From | NikhilS |
|---|---|
| Subject | Re: COPY Transform support |
| Date | |
| Msg-id | d3c4af540804030659h70e1ed5aw57305b0e69e056e@mail.gmail.com Whole thread Raw |
| In response to | COPY Transform support (Dimitri Fontaine <dfontaine@hi-media.com>) |
| Responses |
Re: COPY Transform support
|
| List | pgsql-hackers |
Hi,
+1
Data transformation while doing a data load is a requirement now and then. Considering that users will have to do mass updates *after* the load completes to mend the data to their liking should be reason enough to do this while the loading is happening. I think to go about it the right way we should support the following:
* The ability to provide per-column transformation expressions
COPY mytable (col1 transform to "col1 + 10", col2 transform to "'Post' || 'greSQL'", col3...) FROM ..
* The ability to use any kind of expressions while doing the transformation
The transformation expression should be any expression (basically ExecEvalExpr) that can be evaluated to give a resulting value and obviously a corresponding is_null value too. It should and could be system in-built functions (e.g. UPPER, TRIM, TO_CHAR, TO_NUMBER etc.) or user defined functions too
* The transformation expression can refer to other columns involved in the load. So that when the current row is extracted from the input file, the current values should be used to generate the new resultant values before doing a heap_form_tuple. E.g.
(col1 transform "col1 + 10", col2 transform "col1 * col2", col3 transform "UPPER(col1 || col3)",...)
I have spent some thoughts on how to do this and will be happy to share the same if the list is interested. Personally, I think data transformation using such expressions is a pretty powerful and important activity while doing the data load itself.
Regards,
Nikhils
--
EnterpriseDB http://www.enterprisedb.com
On Thu, Apr 3, 2008 at 6:47 PM, Dimitri Fontaine <dfontaine@hi-media.com> wrote:
Here's a proposal for COPY to support the T part of an ETL, that is adding the
capability for COPY FROM to Transform the data it gets.
The idea is quite simple: adding to COPY FROM the option to run a function on
the data before to call datatype_in functions. This needs some syntax
addition to be worked out at the COPY side, then the COPY code will have to
run the given function on the read data and consider giving the output of it
to current COPY code (datatype input function).
The function could either get the data as text or bytea, and would have to
return either text or bytea. bytea seems the more sensible choice, as long as
we don't lose encoding information there, which I'm not sure about.
The syntax could be something like:
COPY mytable FROM '/my/file.txt' WITH COLUMN x CONVERT USING myfunc;
I tried to only add keywords already present in [1], while getting something
meaningfull... and x is intended to be the column number, counting from 1.
[1] http://www.postgresql.org/docs/8.3/static/sql-keywords-appendix.html
Comments?
--
dim
+1
Data transformation while doing a data load is a requirement now and then. Considering that users will have to do mass updates *after* the load completes to mend the data to their liking should be reason enough to do this while the loading is happening. I think to go about it the right way we should support the following:
* The ability to provide per-column transformation expressions
COPY mytable (col1 transform to "col1 + 10", col2 transform to "'Post' || 'greSQL'", col3...) FROM ..
* The ability to use any kind of expressions while doing the transformation
The transformation expression should be any expression (basically ExecEvalExpr) that can be evaluated to give a resulting value and obviously a corresponding is_null value too. It should and could be system in-built functions (e.g. UPPER, TRIM, TO_CHAR, TO_NUMBER etc.) or user defined functions too
* The transformation expression can refer to other columns involved in the load. So that when the current row is extracted from the input file, the current values should be used to generate the new resultant values before doing a heap_form_tuple. E.g.
(col1 transform "col1 + 10", col2 transform "col1 * col2", col3 transform "UPPER(col1 || col3)",...)
I have spent some thoughts on how to do this and will be happy to share the same if the list is interested. Personally, I think data transformation using such expressions is a pretty powerful and important activity while doing the data load itself.
Regards,
Nikhils
--
EnterpriseDB http://www.enterprisedb.com
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