Fixed bug #21698: erroneously a field could be replaced by an

equal constant under any circumstances.
In fact this substitution can be allowed if the field is
not of a type string or if the field reference serves as 
an argument of a comparison predicate.  


mysql-test/r/func_str.result:
  Added test cases for bug #21698.
mysql-test/r/heap_hash.result:
  Adjusted results after the fix for bug #21198.
mysql-test/t/func_str.test:
  Added test cases for bug #21698.
sql/item.cc:
  Fixed bug #21198.
  Added a method to check whether a field reference can be 
  substituted for a constant equal to the field.
  This substitution is allowed if the field is not of a type string
  or if the field reference serves as an argument of a comparison
  predicate.
sql/item.h:
  Fixed bug #21698.
  Added a new virtual transformation method for a item 'compile'
  with two callback function parameters.
  Added a new virtual method 'subst_argument_checker' to be used
  as an amnalyzer method.
  This method is supposed to set its in/out argument to NULL for
  the nodes where substitution of a string field for a constant
  is not valid.
sql/item_cmpfunc.cc:
  Fixed bug #21698.
  Added an implementation of the compile method for class Item_cond.
  First it processes the Item_cond node with a callback function and if
  the latter returns TRUE it proceeds with a transformation performed by
  another callback function.
sql/item_cmpfunc.h:
  Fixed bug #21698.
  Added the implementations of 'subst_argument_checker'
  for the Item_func and Item_cond classes.
  This method is supposed to set its in/out argument to NULL for
  the nodes where substitution of a string field for a constant
  is not valid.
  Added the declaration of an implementation of the compile method for 
  class Item_cond.
  First it processes the Item_cond node with a callback function and if
  the latter returns TRUE it proceeds with a transformation performed by
  another callback function.
sql/item_func.cc:
  Fixed bug #21698.
  Added an implementation of the compile method for class Item_func.
  First it processes the Item_func node with a callback function and if
  the latter returns TRUE it proceeds with a transformation performed by
  another callback function.
sql/item_func.h:
  Fixed bug #21698.
  Added the declaration of the implementation of the compile method for
  class Item_func.
  First it processes the Item_func node with a callback function and if
  the latter returns TRUE it proceeds with a transformation performed by
  another callback function.
sql/sql_select.cc:
  Fixed bug #21698.
  Limited the conditions at which a field can be substituted 
  a for an equal constant in a formula. 
  This substitution is allowed if the field is not of a type string
  or if the field reference serves as an argument of a comparison
  predicate.

mysql-test/r/func_str.result

@@ -1113,4 +1113,39 @@ conv("18383815659218730760",10,10) + 0
 select "18383815659218730760" + 0;
 "18383815659218730760" + 0
 1.8383815659219e+19
+CREATE TABLE t1 (code varchar(10));
+INSERT INTO t1 VALUES ('a12'), ('A12'), ('a13');
+SELECT ASCII(code), code FROM t1 WHERE code='A12';
+ASCII(code)	code
+97	a12
+65	A12
+SELECT ASCII(code), code FROM t1 WHERE code='A12' AND ASCII(code)=65;
+ASCII(code)	code
+65	A12
+INSERT INTO t1 VALUES ('a12 '), ('A12  ');
+SELECT LENGTH(code), code FROM t1 WHERE code='A12';
+LENGTH(code)	code
+3	a12
+3	A12
+4	a12 
+5	A12  
+SELECT LENGTH(code), code FROM t1 WHERE code='A12' AND LENGTH(code)=5;
+LENGTH(code)	code
+5	A12  
+ALTER TABLE t1 ADD INDEX (code);
+CREATE TABLE t2 (id varchar(10) PRIMARY KEY);
+INSERT INTO t2 VALUES ('a11'), ('a12'), ('a13'), ('a14');
+SELECT * FROM t1 INNER JOIN t2 ON t1.code=t2.id 
+WHERE t2.id='a12' AND (code < 'a00' OR LENGTH(code)=5);
+code	id
+A12  	a12
+EXPLAIN EXTENDED 
+SELECT * FROM t1 INNER JOIN t2 ON code=id 
+WHERE id='a12' AND (code < 'a00' OR LENGTH(code)=5);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	code	code	13	const	3	Using where; Using index
+1	SIMPLE	t2	ref	PRIMARY	PRIMARY	12	const	1	Using where; Using index
+Warnings:
+Note	1003	select `test`.`t1`.`code` AS `code`,`test`.`t2`.`id` AS `id` from `test`.`t1` join `test`.`t2` where ((`test`.`t1`.`code` = _latin1'a12') and (`test`.`t2`.`id` = _latin1'a12') and (length(`test`.`t1`.`code`) = 5))
+DROP TABLE t1,t2;
 End of 5.0 tests

mysql-test/r/heap_hash.result

@@ -354,7 +354,7 @@ t3	1	a	2	b	NULL	13	NULL	NULL		HASH
 explain select * from t1 ignore key(btree_idx), t3 where t1.name='matt' and t3.a = concat('',t1.name) and t3.b=t1.name;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ref	heap_idx	heap_idx	22	const	7	Using where
-1	SIMPLE	t3	ref	a	a	44	const,const	7	Using where
+1	SIMPLE	t3	ref	a	a	44	func,const	7	Using where
 drop table t1, t2, t3;
 create temporary table t1 ( a int, index (a) ) engine=memory;
 insert into t1 values (1),(2),(3),(4),(5);

mysql-test/t/func_str.test

@@ -753,4 +753,31 @@ select cast(rtrim(ltrim('  20.06 ')) as decimal(19,2));
 select conv("18383815659218730760",10,10) + 0;
 select "18383815659218730760" + 0;
 
+#
+# Bug #21698: substitution of a string field for a constant under a function 
+#
+
+CREATE TABLE t1 (code varchar(10));
+INSERT INTO t1 VALUES ('a12'), ('A12'), ('a13');
+
+SELECT ASCII(code), code FROM t1 WHERE code='A12';
+SELECT ASCII(code), code FROM t1 WHERE code='A12' AND ASCII(code)=65;
+
+INSERT INTO t1 VALUES ('a12 '), ('A12  ');
+
+SELECT LENGTH(code), code FROM t1 WHERE code='A12';
+SELECT LENGTH(code), code FROM t1 WHERE code='A12' AND LENGTH(code)=5;
+
+ALTER TABLE t1 ADD INDEX (code);
+CREATE TABLE t2 (id varchar(10) PRIMARY KEY);
+INSERT INTO t2 VALUES ('a11'), ('a12'), ('a13'), ('a14');
+
+SELECT * FROM t1 INNER JOIN t2 ON t1.code=t2.id 
+  WHERE t2.id='a12' AND (code < 'a00' OR LENGTH(code)=5);
+EXPLAIN EXTENDED 
+SELECT * FROM t1 INNER JOIN t2 ON code=id 
+  WHERE id='a12' AND (code < 'a00' OR LENGTH(code)=5);
+
+DROP TABLE t1,t2;
+
 --echo End of 5.0 tests