MonetDB: Jan2014 - fixed over eager rewriting of select distinct.

[Niels Nes]

Changeset: d17ab5825c84 for MonetDB
URL: http://dev.monetdb.org/hg/MonetDB?cmd=changeset;node=d17ab5825c84
Modified Files:
        sql/server/rel_optimizer.c
Branch: Jan2014
Log Message:

fixed over eager rewriting of select distinct.


diffs (33 lines):

diff --git a/sql/server/rel_optimizer.c b/sql/server/rel_optimizer.c
--- a/sql/server/rel_optimizer.c
+++ b/sql/server/rel_optimizer.c
@@ -1953,7 +1953,7 @@ rel_distinct_project2groupby(int *change
        if (rel->op == op_project && rel->l && !rel->r /* no order by */ && 
need_distinct(rel) &&
            exps_card(rel->exps) <= CARD_ATOM) {
                set_nodistinct(rel);
-               rel->l = NULL;
+               rel->l = rel_topn(sql->sa, rel->l, append(sa_list(sql->sa), 
exp_atom_wrd(sql->sa, 1)));
        }
 
        /* rewrite distinct project [ pk ] ( select ( table ) [ e op val ]) 
@@ -1963,8 +1963,8 @@ rel_distinct_project2groupby(int *change
                set_nodistinct(rel);
        /* rewrite distinct project [ gbe ] ( select ( groupby [ gbe ] [ gbe, e 
] )[ e op val ]) 
         * into project [ gbe ] ( select ( group etc ) */
-       if (rel->op == op_project && rel->l && !rel->r /* no order by */ && 
need_distinct(rel) &&
-           l->op == op_select) {
+       if (rel->op == op_project && rel->l && !rel->r /* no order by */ && 
+           need_distinct(rel) && l->op == op_select){ 
                sql_rel *g = l->l;
                if (is_groupby(g->op)) {
                        list *gbe = g->r;
@@ -1989,7 +1989,8 @@ rel_distinct_project2groupby(int *change
                                set_nodistinct(rel);
                }
        }
-       if (rel->op == op_project && rel->l && !rel->r /* no order by */ && 
need_distinct(rel)) {
+       if (rel->op == op_project && rel->l && !rel->r /* no order by */ && 
+           need_distinct(rel) && exps_card(rel->exps) > CARD_ATOM) {
                node *n;
                list *exps = new_exp_list(sql->sa), *gbe = 
new_exp_list(sql->sa);
 
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