Re: WIP patch for LATERAL subqueries

2012/8/6 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>> On 08/05/2012 05:58 PM, Tom Lane wrote:
>>> Currently the patch only implements the syntax called out in the standard,
>>> namely that you can put LATERAL in front of a <derived table>, which is
>>> to say a parenthesized sub-SELECT in FROM. It strikes me that it might be
>>> worth allowing LATERAL with a function-in-FROM as well.
>
>> Pro. As you say this is the main use case, and the longer syntax just
>> seems unnecessary fluff.
>
> After some experimentation it seems that this only works if we promote
> LATERAL to a fully reserved keyword. Apparently the reason is that
> given non-reserved LATERAL followed by an identifier, it's not clear
> without additional lookahead whether we have "LATERAL func_name ..."
> or the LATERAL is a table name and the identifier is an alias. And the
> parser has to make a shift/reduce decision before it can look beyond the
> identifier. (Without the LATERAL func_name syntax, there's no ambiguity
> because LATERAL in its keyword meaning must be immediately followed by a
> left paren.)
>
> Since LATERAL has been a reserved word in every SQL spec since SQL:99,
> I don't feel too bad about making it fully reserved for us too, but
> nonetheless this is a cost of adding this syntax.

+1

Pavel

>
> regards, tom lane
>
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