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The SQL standard does not have general functions-in-FROM, but it does allow UNNEST() there (see the <collection derived table> production), and the semantics of that are defined to include lateral references. So spec compliance requires allowing lateral references within UNNEST() even without an explicit LATERAL keyword. Rather than making UNNEST() a special case, it seems best to extend this flexibility to any function-in-FROM. We'll still allow LATERAL to be written explicitly for clarity's sake, but it's now a noise word in this context. In theory this change could result in a change in behavior of existing queries, by allowing what had been an outer reference in a function-in-FROM to be captured by an earlier FROM-item at the same level. However, all pre-9.3 PG releases have a bug that causes them to match variable references to earlier FROM-items in preference to outer references (and then throw an error). So no previously-working query could contain the type of ambiguity that would risk a change of behavior. Per a suggestion from Andrew Gierth, though I didn't use his patch. |
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