Hello All:
First off, I would like to apologize in case this post does not belong to
this
forum. If that is the case, please let me know if there is another forum
where I
can post my question.
I am writing a parser to parse SQL (actually T-SQL for MS Sql Server). I am
getting a shift/reduce conflict that I don't know how to solve. I know the
reason of the conflict and I can give you 2 valid SQL statements that can be
parsed in two diffrent ways. I just don't know how to solve that in my
grammar.
Consider the following two valid SQL statements:
Statement #1:
select b from s where b not in ( (select a from t where a = 1), 8, 9 );
Statement #2:
select b from s where b not in ( (select a from t where a = 1)
union (select a from t where a = 2)
);
In stmt#1, the search condition inside the "not in" is a list of
expressions.
In stmt#2, the search condition inside the "not in" is another query
combined
with UNION.
Here is a simplified version of my bison grammar:
=========================================================================
expression: ICONST
| expression '+' expression
| expression '-' expression
| expression '*' expression
| expression '/' expression
| expression '%' expression
...
...
| '(' expression ')'
| '(' query_specification ')'
...
...
;
exp_list: exp_list ',' expression
| expression
;
search_condition: expression '>' expression
| expression '<' expression
| expression LIKE expression
...
...
| expression IN '(' exp_list ')'
| expression NOT IN '(' exp_list ')'
| expression IN '(' query_list ')'
| expression NOT IN '(' query_list ')'
...
...
;
query_list: query_list UNION query_list
| '(' query_list ')'
| query_specification
;
/*
* This is the grammar for a select statement
*/
query_specification: SELECT select_list into_clause from_clause
where_clause group_by_clause having_clause
=========================================================================
The ambiguity arise when I give a statement like this:
Statement #3:
select b from s where b not in ( (select a from t where a = 1) );
The parser can treat the search condition as an exp_list or a query_list.
Can someone point me out how to formulate my grammar.
Thanks
Richard
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