Reading from the docs, http://www.postgresql.org/docs/7.4/interactive/sql-select.html
<quote> The optional GROUP BY clause has the general form
GROUP BY expression [, ...]
GROUP BY will condense into a single row all selected rows that share the same values for the grouped expressions. expression can be an input column name, or the name or ordinal number of an output column (SELECT list item), or an arbitrary expression formed from input-column values. In case of ambiguity, a GROUP BY name will be interpreted as an input-column name rather than an output column name.
Aggregate functions, if any are used, are computed across all rows making up each group, producing a separate value for each group (whereas without GROUP BY, an aggregate produces a single value computed across all the selected rows). When GROUP BY is present, it is not valid for the SELECT list expressions to refer to ungrouped columns except within aggregate functions, since there would be more than one possible value to return for an ungrouped column.
</quote>
John Sidney-Woollett
Joost Kraaijeveld wrote:
Hi John,
John Sidney-Woollett schreef:
Useful to add a title to your messages before you post...
It escaped before finishing.....
How about:
select parentid, count(*) as number_of_children from childtable group by parentid order by parentid;
It works but can you tell me why this works? Is the count(*) over the "group by parentid"?
Groeten,
Joost Kraaijeveld Askesis B.V. Molukkenstraat 14 6524NB Nijmegen tel: 024-3888063 / 06-51855277 fax: 024-3608416 e-mail: [EMAIL PROTECTED] web: www.askesis.nl
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