对于PostgreSQL的语法分析，修改其 gram.y后，
opt_distinct:
DISTINCT { $$ = list_make1(NIL); }
| DISTINCT ON '(' expr_list ')' { $$ = $4; }
| ALL { $$ = NIL; }
| /*EMPTY*/ { $$ = NIL; }
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simple_select:
SELECT opt_distinct target_list
into_clause from_clause where_clause
group_clause having_clause window_clause
{
SelectStmt *n = makeNode(SelectStmt);
n->distinctClause = $2;
n->targetList = $3;
n->intoClause = $4;
n->fromClause = $5;
n->whereClause = $6;
n->groupClause = $7;
n->havingClause = $8;
n->windowClause = $9;
$$ = (Node *)n;
}
| values_clause { $$ = $1; }
| TABLE relation_expr
{
/* same as SELECT * FROM relation_expr */
ColumnRef *cr = makeNode(ColumnRef);
ResTarget *rt = makeNode(ResTarget);
SelectStmt *n = makeNode(SelectStmt);
cr->fields = list_make1(makeNode(A_Star));
cr->location = -1;
rt->name = NULL;
rt->indirection = NIL;
rt->val = (Node *)cr;
rt->location = -1;
n->targetList = list_make1(rt);
n->fromClause = list_make1($2);
$$ = (Node *)n;
}
| select_clause UNION opt_all select_clause
{
$$ = makeSetOp(SETOP_UNION, $3, $1, $4);
}
| select_clause INTERSECT opt_all select_clause
{
$$ = makeSetOp(SETOP_INTERSECT, $3, $1, $4);
}
| select_clause EXCEPT opt_all select_clause
{
$$ = makeSetOp(SETOP_EXCEPT, $3, $1, $4);
}
;
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-->
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opt_distinct:
DISTINCT { $$ = list_make1(NIL);
fprintf(stderr,"In opt_distinct\n");
}
| DISTINCT ON '(' expr_list ')' { $$ = $4; }
| ALL { $$ = NIL; }
| /*EMPTY*/ { $$ = NIL; }
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-->
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simple_select:
SELECT opt_distinct target_list
into_clause from_clause where_clause
group_clause having_clause window_clause
{
SelectStmt *n = makeNode(SelectStmt);
n->distinctClause = $2;
n->targetList = $3;
n->intoClause = $4;
n->fromClause = $5;
n->whereClause = $6;
n->groupClause = $7;
n->havingClause = $8;
n->windowClause = $9;
$$ = (Node *)n;
fprintf(stderr,"In simple select\n“);
}
| values_clause { $$ = $1; }
| TABLE relation_expr
{
/* same as SELECT * FROM relation_expr */
ColumnRef *cr = makeNode(ColumnRef);
ResTarget *rt = makeNode(ResTarget);
SelectStmt *n = makeNode(SelectStmt);
cr->fields = list_make1(makeNode(A_Star));
cr->location = -1;
rt->name = NULL;
rt->indirection = NIL;
rt->val = (Node *)cr;
rt->location = -1;
n->targetList = list_make1(rt);
n->fromClause = list_make1($2);
$$ = (Node *)n;
}
| select_clause UNION opt_all select_clause
{
$$ = makeSetOp(SETOP_UNION, $3, $1, $4);
}
| select_clause INTERSECT opt_all select_clause
{
$$ = makeSetOp(SETOP_INTERSECT, $3, $1, $4);
}
| select_clause EXCEPT opt_all select_clause
{
$$ = makeSetOp(SETOP_EXCEPT, $3, $1, $4);
}
;
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在psql执行查询：select distinct id from a6;
在后台会显示：
In opt_distinct
In simple select
本文转自健哥的数据花园博客园博客，原文链接：http://www.cnblogs.com/gaojian/archive/2012/09/05/2671715.html，如需转载请自行联系原作者
