Bug#34787357 Hypergraph: row estimates for field=non_field_term ignores indexes and histogram

Post-push fix: The initial commit triggers an assert for "reversed"
conditions, e.g. expression=field_with_histogram (while
field_with_histogram=expression does not).

This commit adds new test cases and a fix for that issue.

Change-Id: I48e6a51417135c2d868e839ac92458d68958ed7e

Author: Jan Wedvik

mysql-test/r/hypergraph_bugs.result

@@ -949,6 +949,11 @@ EXPLAIN
 -> Filter: (t1.c = floor(rand(0)))  (rows=16) (actual rows=16 loops=1)
     -> Table scan on t1  (rows=256) (actual rows=256 loops=1)
 
+EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE FLOOR(RAND(0))=c;
+EXPLAIN
+-> Filter: (floor(rand(0)) = t1.c)  (rows=16) (actual rows=16 loops=1)
+    -> Table scan on t1  (rows=256) (actual rows=256 loops=1)
+
 EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE d=FLOOR(RAND(0));
 EXPLAIN
 -> Filter: (t1.d = floor(rand(0)))  (rows=4) (actual rows=16 loops=1)
@@ -999,6 +1004,11 @@ EXPLAIN
 -> Filter: (t1.c <> floor(rand(0)))  (rows=240) (actual rows=240 loops=1)
     -> Table scan on t1  (rows=256) (actual rows=256 loops=1)
 
+EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE FLOOR(RAND(0))<>c;
+EXPLAIN
+-> Filter: (floor(rand(0)) <> t1.c)  (rows=240) (actual rows=240 loops=1)
+    -> Table scan on t1  (rows=256) (actual rows=256 loops=1)
+
 EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE b<>(SELECT MIN(b) FROM t1);
 EXPLAIN
 -> Filter: (t1.b <> (select #2))  (rows=240) (actual rows=240 loops=1)

mysql-test/t/hypergraph_bugs.test

@@ -781,6 +781,11 @@ EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE b=FLOOR(RAND(0));
 --replace_regex $elide_costs_and_time
 EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE c=FLOOR(RAND(0));
 
+# Make estimate from histogram, even if value is unknown. Note that the field
+# is on the right hand side of '='.
+--replace_regex $elide_costs_and_time
+EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE FLOOR(RAND(0))=c;
+
 # Make estimate from second field of index. Since 'b' and 'd' are independent,
 # the estimate will be too low.
 --replace_regex $elide_costs_and_time
@@ -824,6 +829,11 @@ EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE b<>FLOOR(RAND(0));
 --replace_regex $elide_costs_and_time
 EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE c<>FLOOR(RAND(0));
 
+# Make estimate from histogram, even if value is unknown. Note that the field
+# is on the right hand side of '<>'.
+--replace_regex $elide_costs_and_time
+EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE FLOOR(RAND(0))<>c;
+
 # Make estimate from index, even if value is unknown.
 --replace_regex $elide_costs_and_time
 EXPLAIN ANALYZE SELECT 1 FROM t1 WHERE b<>(SELECT MIN(b) FROM t1);

sql/histograms/histogram.cc

@@ -1964,12 +1964,13 @@ bool Histogram::get_raw_selectivity(Item **items, size_t item_count,
       assert(item_count == 2);
       /*
         Verify that one side of the predicate is a column/field, and that the
-        other side is a constant value.
+        other side is a constant value (except for EQUALS_TO and NOT_EQUALS_TO).
 
-        Make sure that we have the constant item as the right side argument of
+        Make sure that we have the field item as the left side argument of
         the predicate internally.
       */
-      if (items[0]->const_item() && items[1]->type() == Item::FIELD_ITEM) {
+      if (items[0]->type() != Item::FIELD_ITEM &&
+          items[1]->type() == Item::FIELD_ITEM) {
         // Flip the operators as well as the operator itself.
         switch (op) {
           case enum_operator::GREATER_THAN:
@@ -1991,10 +1992,9 @@ bool Histogram::get_raw_selectivity(Item **items, size_t item_count,
         items_flipped[0] = items[1];
         items_flipped[1] = items[0];
         return get_selectivity(items_flipped, item_count, op, selectivity);
-      } else if ((items[0]->type() != Item::FIELD_ITEM ||
-                  !items[1]->const_item()) &&
-                 op != enum_operator::EQUALS_TO &&
-                 op != enum_operator::NOT_EQUALS_TO) {
+      } else if (items[0]->type() != Item::FIELD_ITEM ||
+                 (!items[1]->const_item() && op != enum_operator::EQUALS_TO &&
+                  op != enum_operator::NOT_EQUALS_TO)) {
         return true;
       }
       break;