MDEV-13897 SELECT @A := MAX(col) FROM t requires full index scan

fix some old bad merge

mysql-test/r/join_cache.result

@@ -5880,7 +5880,7 @@ where c1 = c2-0 and c2 <= (select max(c3) from t3 where c3 = 2 and @counter:=@co
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; Using join buffer (flat, BNL join)
-2	UNCACHEABLE SUBQUERY	t3	system	NULL	NULL	NULL	NULL	1	
+2	UNCACHEABLE SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 set @counter=0;
 select count(*) from t1 straight_join t2
 where c1 = c2-0 and c2 <= (select max(c3) from t3 where c3 = 2 and @counter:=@counter+1);

mysql-test/r/user_var.result

-drop table if exists t1,t2;
 set @a := foo;
 ERROR 42S22: Unknown column 'foo' in 'field list'
 set @a := connection_id() + 3;
@@ -126,14 +125,14 @@ select @a+0, @a:=@a+0+count(*), count(*), @a+0 from t1 group by i;
 set @a=0;
 select @a,@a:="hello",@a,@a:=3,@a,@a:="hello again" from t1 group by i;
 @a	@a:="hello"	@a	@a:=3	@a	@a:="hello again"
-0	hello	0	3	3	hello again
-0	hello	0	3	3	hello again
-0	hello	0	3	3	hello again
+0	hello	0	3	0	hello again
+0	hello	0	3	0	hello again
+0	hello	0	3	0	hello again
 select @a,@a:="hello",@a,@a:=3,@a,@a:="hello again" from t1 group by i;
 @a	@a:="hello"	@a	@a:=3	@a	@a:="hello again"
-hello again	hello	hello	3	3	hello again
-hello again	hello	hello	3	3	hello again
-hello again	hello	hello	3	3	hello again
+hello again	hello	hello again	3	hello again	hello again
+hello again	hello	hello again	3	hello again	hello again
+hello again	hello	hello again	3	hello again	hello again
 drop table t1;
 set @a=_latin2'test';
 select charset(@a),collation(@a),coercibility(@a);
@@ -570,3 +569,6 @@ End of 5.5 tests
 #
 set @var= repeat('a',20000);
 1
+explain select @a:=max(seq) from seq_1_to_1000000;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away

mysql-test/r/variables.result

@@ -1544,7 +1544,7 @@ one
 1
 explain SELECT 1 as 'one' FROM t1 GROUP BY @a:= (SELECT ROUND(f1) FROM t1 WHERE f1 = 0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	
 2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
 SELECT 1 as 'one' FROM t1 GROUP BY @a:= (SELECT ROUND(f1) FROM t1 WHERE f1 = 0);
 one
@@ -1555,7 +1555,7 @@ one
 set sql_buffer_result=1;
 explain SELECT 1 as 'one' FROM t1 GROUP BY @a:= (SELECT ROUND(f1) FROM t1 WHERE f1 = 0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary
 2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
 SELECT 1 as 'one' FROM t1 GROUP BY @a:= (SELECT ROUND(f1) FROM t1 WHERE f1 = 0);
 one

mysql-test/t/user_var.test

 # Initialise
---disable_warnings
-drop table if exists t1,t2;
---enable_warnings
+source include/have_sequence.inc;
 
 --error 1054
 set @a := foo;
@@ -501,3 +499,9 @@ eval select $tmp < $tmp2;
 --enable_column_names
 --enable_query_log
 
+#
+# MDEV-13897 SELECT @a := MAX(col) FROM t requires full index scan
+#
+explain select @a:=max(seq) from seq_1_to_1000000;
+
+# End of 10.1 tests

sql/item_func.h

@@ -1773,12 +1773,6 @@ class Item_func_set_user_var :public Item_func_user_var
            create_tmp_field(false, table, MY_INT32_NUM_DECIMAL_DIGITS) :
            tmp_table_field_from_field_type(table, false, true);
   }
-  table_map used_tables() const
-  {
-    return used_tables_cache | RAND_TABLE_BIT;
-  }
-  bool const_item() const { return 0; }
-  bool is_expensive() { return 1; }
   virtual void print(String *str, enum_query_type query_type);
   void print_as_stmt(String *str, enum_query_type query_type);
   const char *func_name() const { return "set_user_var"; }