Sergei Golubchik wrote:
> Hi!
>
> On Dec 10, Davi Arnaut wrote:
>> Sergei Golubchik wrote:
>>> On Dec 10, Davi Arnaut wrote:
>>>> ChangeSet@stripped, 2007-12-10 11:34:12-02:00, davi@stripped +7 -0
>>>> Bug#28317 Left Outer Join with {oj outer-join}
>>>>
>>>> Parser rejects ODBC's escape sequences for outer joins other than
>>>> left outer join, yet the escape sequence BNF specifies that this
>>>> syntax can be used for left, right, and full outer join syntax.
>>> Why not to do it in the parser ? Lexer's task, conceptually, is to
>>> split the input stream of characters into a stream of lexems. And
>>> parser is supposed to apply grammar rules to the that.
>> Practically speaking, because it introduces complexity and conflicts
>> to the parser for something that in the first place shouldn't be
>> handled by the server parser.
>
> What complexity and conflicts ? '{' isn't used anywhere in SQL, there
> could be no ambiguity.
Look at the patch. See the rule for the left outer join.
>> Conceptually speaking, a Lexer task is to do lexical analysis which is
>> a "tokenization" process, but it doesn't me it must convert all
>> characters into tokens. If the "lexeme" doesn't have any meaning,
>> there is no point in passing it to the parser. This is quite common,
>> you don't see parsers taking whitespace and comments into account.
>
> Whitespace and comments - yes. But here there're three tokens: '{' 'oj'
> ... '}' separated by other meaningful tokens. You cannot match and
> remove them in a lexer, only a parser can do that. You can pretend that
> lexer does it, but in fact it does it by embedding a simple parser,
> that's all.
>
> To prove the point - your patch doesn't work, it doesn't handle nested
> escapes, as far as I can see:
>
> SELECT ... FROM {oj t1 LEFT JOIN {oj t2 LEFT JOIN t3}}
> SELECT ... FROM {oj t1 LEFT JOIN (SELECT * FROM {oj t2 LEFT JOIN t3})}
And that was intentional, why should we support nested escapes?
Regards,
--
Davi Arnaut, Software Engineer
MySQL Inc, www.mysql.com
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