Fix for bug#49517: Inconsistent behavior while using

NULLable BIGINT and INT columns in comparison

Problem: a consequence of the fix for 43668.
Some Arg_comparator inner initialization missed,
that may lead to unpredictable (wrong) comparison
results.

Fix: always properly initialize Arg_comparator
before its usage.

Author: Ramil Kalimullin

mysql-test/r/select.result

@@ -4619,4 +4619,19 @@ c1
 9.1234
 DROP TABLE t1;
 # End of test for bug#49489.
+#
+# Bug #49517: Inconsistent behavior while using 
+# NULLable BIGINT and INT columns in comparison
+#
+CREATE TABLE t1(a BIGINT UNSIGNED NOT NULL, b BIGINT NULL, c INT NULL);
+INSERT INTO t1 VALUES(105, NULL, NULL);
+SELECT * FROM t1 WHERE b < 102;
+a	b	c
+SELECT * FROM t1 WHERE c < 102;
+a	b	c
+SELECT * FROM t1 WHERE 102 < b;
+a	b	c
+SELECT * FROM t1 WHERE 102 < c;
+a	b	c
+DROP TABLE t1;
 End of 5.1 tests

mysql-test/t/select.test

@@ -3973,4 +3973,18 @@ SELECT * FROM t1 WHERE c1 < 9.12345;
 DROP TABLE t1;
 --echo # End of test for bug#49489.
 
+
+--echo #
+--echo # Bug #49517: Inconsistent behavior while using 
+--echo # NULLable BIGINT and INT columns in comparison
+--echo #
+CREATE TABLE t1(a BIGINT UNSIGNED NOT NULL, b BIGINT NULL, c INT NULL);
+INSERT INTO t1 VALUES(105, NULL, NULL);
+SELECT * FROM t1 WHERE b < 102;
+SELECT * FROM t1 WHERE c < 102;
+SELECT * FROM t1 WHERE 102 < b;
+SELECT * FROM t1 WHERE 102 < c;
+DROP TABLE t1;
+
+
 --echo End of 5.1 tests

sql/item_cmpfunc.cc

@@ -895,9 +895,9 @@ int Arg_comparator::set_cmp_func(Item_result_field *owner_arg,
   ulonglong const_value= (ulonglong)-1;
   thd= current_thd;
   owner= owner_arg;
+  set_null= set_null && owner_arg;
   a= a1;
   b= a2;
-  owner= owner_arg;
   thd= current_thd;
 
   if ((cmp_type= can_compare_as_dates(*a, *b, &const_value)))

sql/item_cmpfunc.h

@@ -54,10 +54,10 @@ class Arg_comparator: public Sql_alloc
   /* Allow owner function to use string buffers. */
   String value1, value2;
 
-  Arg_comparator(): thd(0), a_cache(0), b_cache(0), set_null(0),
+  Arg_comparator(): thd(0), a_cache(0), b_cache(0), set_null(TRUE),
     get_value_a_func(0), get_value_b_func(0) {};
   Arg_comparator(Item **a1, Item **a2): a(a1), b(a2), thd(0),
-    a_cache(0), b_cache(0), set_null(0),
+    a_cache(0), b_cache(0), set_null(TRUE),
     get_value_a_func(0), get_value_b_func(0) {};
 
   int set_compare_func(Item_result_field *owner, Item_result type);