Changeset: 2b345d7a347d for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB/rev/2b345d7a347d
Modified Files:
sql/server/rel_optimize_proj.c
Branch: const_aggr_elim
Log Message:
Adds some comments for clarity
diffs (54 lines):
diff --git a/sql/server/rel_optimize_proj.c b/sql/server/rel_optimize_proj.c
--- a/sql/server/rel_optimize_proj.c
+++ b/sql/server/rel_optimize_proj.c
@@ -2515,6 +2515,11 @@ rel_remove_const_aggr(visitor *v, sql_re
}
if(!list_empty(rel->r)) {
+ /* in the general case in an expression of an aggregate over
+ * a constant can be rewritten as just the const e.g.
+ * aggr(const) -> const
+ */
+
for(node *n = exps->h; n; n = n->next) {
sql_exp *e = n->data;
@@ -2524,11 +2529,17 @@ rel_remove_const_aggr(visitor *v, sql_re
sql_func *j = ((sql_subfunc *)e->f)->func;
+ /* some aggregates with const values can only be
eliminated
+ * under certain circumstances e.g.
+ * sum(NULL) -> NULL, sum(0) -> 0
+ * prod(NULL) -> NULL, prod(1) -> 1
+ * count(NULL) -> 0
+ */
int sum = strcmp(j->base.name, "sum") == 0,
prd = strcmp(j->base.name, "prod") == 0,
cnt = strcmp(j->base.name, "count") == 0;
- if(!j->s && j->system == 1) { // && !cnt
+ if(!j->s && j->system == 1) {
list *se = e->l;
if(se == NULL) {
@@ -2549,7 +2560,6 @@ rel_remove_const_aggr(visitor *v, sql_re
continue;
}
- /* Handle: select
count(distinct NULL) + 3 == 3 */
if(cnt) {
if(wa->isnull) {
list_remove_node(se, NULL, m);
@@ -2572,9 +2582,9 @@ rel_remove_const_aggr(visitor *v, sql_re
}
}
- /*
+ /*
* Below code replaces GROUP BY with PROJECT in some cases;
- * Triggers on...
+ * Triggers on...
* select 1 having true; select 42 from foo group by x; select n from
foo group by rollup(n);
*/
_______________________________________________
checkin-list mailing list -- [email protected]
To unsubscribe send an email to [email protected]
