Fixed mdev-14947 Assertion `0' fails in Field_null::can_optimize_keypart_ref

when number of NULLs in IN list reaches in_predicate_conversion_threshold

The bug was fixed by removing an assertion that had been set in order
just to test whether the code could be ever executed.

mysql-test/r/opt_tvc.result

@@ -614,3 +614,27 @@ Warnings:
 Note	1003	/* select#1 */ select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` where !<expr_cache><`test`.`t2`.`a`,`test`.`t2`.`c`>(<in_optimizer>((`test`.`t2`.`a`,`test`.`t2`.`c`),(`test`.`t2`.`a`,`test`.`t2`.`c`) in ( <materialize> (/* select#2 */ select `tvc_0`.`1`,`tvc_0`.`2` from (values (1,2),(8,9),(5,1)) `tvc_0` ), <primary_index_lookup>(`test`.`t2`.`a` in <temporary table> on distinct_key where `test`.`t2`.`a` = `<subquery2>`.`1` and `test`.`t2`.`c` = `<subquery2>`.`2`))))
 drop table t1, t2, t3;
 set @@in_predicate_conversion_threshold= default;
+#
+# MDEV-14947: conversion of TVC with only NULL values
+#
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (3), (2), (7);
+SELECT * FROM t1 WHERE i IN (NULL, NULL, NULL, NULL, NULL);
+i
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE i IN (NULL, NULL, NULL, NULL, NULL);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`i` AS `i` from `test`.`t1` where `test`.`t1`.`i` in (NULL,NULL,NULL,NULL,NULL)
+SET in_predicate_conversion_threshold= 5;
+SELECT * FROM t1 WHERE i IN (NULL, NULL, NULL, NULL, NULL);
+i
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE i IN (NULL, NULL, NULL, NULL, NULL);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	
+1	PRIMARY	<derived3>	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where; FirstMatch(t1); Using join buffer (flat, BNL join)
+3	DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+Warnings:
+Note	1003	/* select#1 */ select `test`.`t1`.`i` AS `i` from `test`.`t1` semi join ((values (NULL),(NULL),(NULL),(NULL),(NULL)) `tvc_0`) where `test`.`t1`.`i` = `tvc_0`.`NULL`
+SET in_predicate_conversion_threshold= default;
+DROP TABLE t1;

mysql-test/t/opt_tvc.test

@@ -318,3 +318,25 @@ eval explain extended $query;
 drop table t1, t2, t3;
 
 set @@in_predicate_conversion_threshold= default;
+
+--echo #
+--echo # MDEV-14947: conversion of TVC with only NULL values
+--echo #
+
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (3), (2), (7);
+
+let $q=
+SELECT * FROM t1 WHERE i IN (NULL, NULL, NULL, NULL, NULL);
+
+eval $q;
+eval EXPLAIN EXTENDED $q;
+
+SET in_predicate_conversion_threshold= 5;
+
+eval $q;
+eval EXPLAIN EXTENDED $q;
+
+SET in_predicate_conversion_threshold= default;
+
+DROP TABLE t1;

sql/field.h

@@ -2372,13 +2372,11 @@ class Field_null :public Field_str {
   bool can_optimize_keypart_ref(const Item_bool_func *cond,
                                 const Item *item) const
   {
-    DBUG_ASSERT(0);
     return false;
   }
   bool can_optimize_group_min_max(const Item_bool_func *cond,
                                   const Item *const_item) const
   {
-    DBUG_ASSERT(0);
     return false;
   }
 };