Bug #32942 now() - interval '7200' second NOT pre-calculated, causing "full table scan"

Problem is not about intervals and doesn't actually cause 'full table scan'.
We have an optimization for DISTINCT when we have
'DISTINCT field_from_first_join_table' we don't need to read all the
rows from the JOIN-ed table if we found one conforming row.
It stopped working in 5.0 as we return NESTED_LOOP_OK if we came upon
that case in the evaluate_join_record() and that doesn't break the
recordreading loop in sub_select().

Fixed by returning NESTED_LOOP_NO_MORE_ROWS in this case.

mysql-test/r/select.result

@@ -4328,4 +4328,25 @@ SELECT * FROM t1 WHERE c1 > NULL + 1;
 c1
 DROP TABLE t1;
 
+CREATE TABLE t1 (a INT, b INT);
+CREATE TABLE t2 (a INT, c INT, KEY(a));
+INSERT INTO t1 VALUES (1, 1), (2, 2);
+INSERT INTO t2 VALUES (1, 1), (1, 2), (1, 3), (1, 4), (1, 5),
+(2, 1), (2, 2), (2, 3), (2, 4), (2, 5),
+(3, 1), (3, 2), (3, 3), (3, 4), (3, 5),
+(4, 1), (4, 2), (4, 3), (4, 4), (4, 5);
+FLUSH STATUS;
+SELECT DISTINCT b FROM t1 LEFT JOIN t2 USING(a) WHERE c <= 3;
+b
+1
+2
+SHOW STATUS LIKE 'Handler_read%';
+Variable_name	Value
+Handler_read_first	0
+Handler_read_key	2
+Handler_read_next	0
+Handler_read_prev	0
+Handler_read_rnd	0
+Handler_read_rnd_next	6
+DROP TABLE t1, t2;
 End of 5.0 tests

mysql-test/t/select.test

@@ -3672,4 +3672,22 @@ DROP TABLE t1;
 
 --echo
 
+#
+# Bug #32942 now() - interval '7200' second is NOT pre-calculated, causing "full table scan"
+#
+
+CREATE TABLE t1 (a INT, b INT);
+CREATE TABLE t2 (a INT, c INT, KEY(a));
+
+INSERT INTO t1 VALUES (1, 1), (2, 2);
+INSERT INTO t2 VALUES (1, 1), (1, 2), (1, 3), (1, 4), (1, 5),
+                      (2, 1), (2, 2), (2, 3), (2, 4), (2, 5),
+                      (3, 1), (3, 2), (3, 3), (3, 4), (3, 5),
+                      (4, 1), (4, 2), (4, 3), (4, 4), (4, 5);
+
+FLUSH STATUS;
+SELECT DISTINCT b FROM t1 LEFT JOIN t2 USING(a) WHERE c <= 3;
+SHOW STATUS LIKE 'Handler_read%';
+DROP TABLE t1, t2;
+
 --echo End of 5.0 tests

sql/sql_select.cc

@@ -10791,7 +10791,7 @@ evaluate_join_record(JOIN *join, JOIN_TAB *join_tab,
         we found a row, as no new rows can be added to the result.
       */
       if (not_used_in_distinct && found_records != join->found_records)
-        return NESTED_LOOP_OK;
+        return NESTED_LOOP_NO_MORE_ROWS;
     }
     else
       join_tab->read_record.file->unlock_row();