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This article introduces the knowledge of "how to use the PostgreSQL lexical grammar parser to associate with dblink". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Yesterday, someone said that they didn't understand what was going on with that Op. Let's get it straight again. The code is under src/backend/parser, open them to taste carefully, very simple.

Scan.l is very different from gram.y, of course, the former is a flex script, while the latter is a yacc script; the former is lexical analysis, while the latter is parsing.

Let's take a look at the operator definition in scan.l. It consists of one or more of the following characters: ~! @ # ^ & `? +-* /% =. That's why we say that table_remote@dblink should be defined by operators, while other characters can be used directly, such as name_list', 'name. Here a comma can be used as a grammatical element because it does not appear in the list of characters defined by the lexical engine.

Op_chars [\ ~\!\ @\\ ^\ &\ |\ `\?\ +\ -\ *\ /\%\ =] operator {op_chars} +

Moving on, the code for operator in scan.l:

{operator} {(. ) yylval- > str = pstrdup (yytext); return Op;}

This determines whether the character sequence is Op, and if so, gram.y is instructed: the next token is Op.

Op can find the definition in the gram.h generated by gram.y:

# define Op 263

You can also know whether the token is @ in gram. String comparison is fine, because that's how it is defined in gram.y:

% token IDENT FCONST SCONST BCONST XCONST Op

More articles:

IBM "getting started with Yacc and Lex"

Google, Bing

Books

"lex and yacc"

I don't know how else to be more detailed. If I see more and understand more, I will know.

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