On 11 Feb 2009, at 00:03, Tom Lane <t...@sss.pgh.pa.us> wrote:
Actually, that makes less sense than the antijoin case. For antijoin
there is a well-defined value for the extended columns, ie null. For
a semijoin the RHS values might come from any of the rows that happen
to join to the current LHS row, so I'm just as happy that it's
syntactically impossible to reference them.
Actually I think the way mysql users used to spell EXISTS/IN before
mysql supported them would qualify as a semijoin where you can access
the columns:
SELECT distinct a.* from a,b WHERE a.id = b.id
To access columns from b in postgres you would have to use DISTINCT ON.
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