Обсуждение: gram.y
Hi all, I'm trying to make parser recognize SELECTs between parenthesis. I need to do this work to have m$access working with PostgreSQL. The micro$oft access jet (great wisdom) translates the UNIONs as: (SELECT ...) UNION (SELECT ...) To have PostgreSQL understand this syntax I edited gram.y and I modified the "SelectStmt:" and the "SubUnion:" as: SelectStmt: opt_left_paren SELECT opt_unique res_target_list2 result from_clause where_clause group_clause having_clause opt_right_paren union_clause sort_clause { SelectStmt *n =makeNode(SelectStmt); n->unique = $3; n->targetList = $4; n->into = $5; n->fromClause = $6; n->whereClause = $7; n->groupClause = $8; n->havingClause = $9; n->unionClause = $11; n->sortClause = $12; $$ = (Node *)n; } ; SubUnion: opt_left_paren SELECT opt_unique res_target_list2 from_clause where_clause group_clause having_clause opt_right_paren { SelectStmt *n = makeNode(SelectStmt); n->unique = $3; n->unionall = FALSE; n->targetList = $4; n->fromClause = $5; n->whereClause = $6; n->groupClause = $7; n->havingClause = $8; $$ = (Node *)n; } ; and now with these changes I can specify SELECTs inside () and without parenthesis as before, I tried also subselects and seems that all works well...but when I tried a select with a function which contains parenthesis, like SUM(), VERSION() for example, then it doesn't work anymore. I'm not very good programing in C. Is there anybody that can help me with this question ? Any help would be very appreciated. EXAMPLES: (select (2-3)*3); ?column? -------- -3 (1 row) (select (132-3)*3) union all ( select ((983+1)/2) ); ?column? -------- 387 492 (2 rows) select (132-3)*3 union all select ((983+1)/2); ?column? -------- 387 492 (2 rows) select ename from emp where ename in ( select ename from emp where ename like 'K%' ); ename ----- KING (1 row) select version(); ERROR: parser: parse error at or near "(" -Jose'-
> I'm trying to make parser recognize SELECTs between parenthesis. > I need to do this work to have m$access working with PostgreSQL. > The micro$oft access jet (great wisdom) translates the UNIONs as: > (SELECT ...) UNION (SELECT ...) OK, just assume I have mentioned that you should ask M$ to support standard syntax. It isn't entirely clear from the BNF definition of SQL92 (parens near SELECT are allowed in some places), but I was hard pressed to see where this was legal syntax. > To have PostgreSQL understand this syntax I edited gram.y > and I modified the "SelectStmt:" and the "SubUnion:" as: > SelectStmt: opt_left_paren SELECT <snip> One problem with this is the parens must of course be balanced, so making them individually optional is probably not the right thing to do. Just to experiment I tried adding parens on some of the several places where selects with unions are allowed, and started running into trouble on the second one I tried. I'm guessing that a yacc-based parser will run into serious trouble, but I haven't thought of a completely fatal example yet. Also, the way gram.y is currently laid out it would be difficult to ensure that all clauses of the UNION are surrounded by parens if one clause has those parens. But I think this would be desirable if the parens are going to be allowed at all. - Tom
Hello Thomas, domenica, 6 dicembre 98, you wrote: >> I'm trying to make parser recognize SELECTs between parenthesis. >> I need to do this work to have m$access working with PostgreSQL. >> The micro$oft access jet (great wisdom) translates the UNIONs as: >> (SELECT ...) UNION (SELECT ...) TGL> OK, just assume I have mentioned that you should ask M$ to support TGL> standard syntax. It isn't entirely clear from the BNF definition of TGL> SQL92 (parens near SELECT are allowed in some places), but I was hard TGL> pressed to see where this was legal syntax. The problem is: I can't say this syntax is illegal, I can't find nothing about it on SQL documentation. Any way. I think it would be interesting to have parser recognize every statement enclosed into parens. I have also Informix-SE on my Linux box, I tried statements enclosed into parens and Informix understand it. -Jose'-