MDEV-8705 Wrong result for SELECT..WHERE latin1_bin_column='a' AND latin1_bin_column='A'

MDEV-8712 Wrong result for SELECT..WHERE latin1_bin_column=_latin1'a' AND latin1_bin_column='A'

mysql-test/r/ctype_latin1.result

@@ -8149,5 +8149,24 @@ Warnings:
 Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = 'a') and (length(`test`.`t1`.`a`) = 2))
 DROP TABLE t1;
 #
+# MDEV-8712 Wrong result for SELECT..WHERE latin1_bin_column=_latin1'a' AND latin1_bin_column='A'
+#
+SET NAMES latin1;
+CREATE TABLE t1 (a VARCHAR(20) COLLATE latin1_bin);
+INSERT INTO t1 VALUES ('a'),('b');
+SELECT * FROM t1 WHERE a='A';
+a
+SELECT * FROM t1 WHERE a='A' AND a=_latin1'a';
+a
+SELECT * FROM t1 WHERE a=_latin1'a' AND a='A';
+a
+SELECT * FROM t1 WHERE a=_latin1'A';
+a
+SELECT * FROM t1 WHERE a=_latin1'A' AND a=_latin1'a';
+a
+SELECT * FROM t1 WHERE a=_latin1'a' AND a=_latin1'A';
+a
+DROP TABLE t1;
+#
 # End of 10.1 tests
 #

mysql-test/r/ctype_uca.result

@@ -13709,5 +13709,22 @@ SELECT '10' COLLATE utf8_general_ci XOR '20' COLLATE utf8_unicode_ci;
 '10' COLLATE utf8_general_ci XOR '20' COLLATE utf8_unicode_ci
 0
 #
+# MDEV-8705 Wrong result for SELECT..WHERE latin1_bin_column='a' AND latin1_bin_column='A'
+#
+SET NAMES utf8 COLLATE utf8_german2_ci;
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET utf8 COLLATE utf8_bin);
+INSERT INTO t1 VALUES ('a'),('A');
+SELECT * FROM t1 WHERE a='a';
+a
+a
+SELECT * FROM t1 WHERE a=_utf8'a';
+a
+a
+SELECT * FROM t1 WHERE a='a' AND a=_utf8'a';
+a
+a
+DROP TABLE t1;
+SET NAMES utf8;
+#
 # End of MariaDB-10.1 tests
 #

mysql-test/t/ctype_latin1.test

@@ -349,6 +349,19 @@ SELECT * FROM t1 WHERE a='a' AND LENGTH(a)=2;
 EXPLAIN EXTENDED SELECT * FROM t1 WHERE a='a' AND LENGTH(a)=2;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-8712 Wrong result for SELECT..WHERE latin1_bin_column=_latin1'a' AND latin1_bin_column='A'
+--echo #
+SET NAMES latin1;
+CREATE TABLE t1 (a VARCHAR(20) COLLATE latin1_bin);
+INSERT INTO t1 VALUES ('a'),('b');
+SELECT * FROM t1 WHERE a='A';
+SELECT * FROM t1 WHERE a='A' AND a=_latin1'a';
+SELECT * FROM t1 WHERE a=_latin1'a' AND a='A';
+SELECT * FROM t1 WHERE a=_latin1'A';
+SELECT * FROM t1 WHERE a=_latin1'A' AND a=_latin1'a';
+SELECT * FROM t1 WHERE a=_latin1'a' AND a=_latin1'A';
+DROP TABLE t1;
 
 --echo #
 --echo # End of 10.1 tests

mysql-test/t/ctype_uca.test

@@ -630,6 +630,18 @@ DROP TABLE t1;
 --echo #
 SELECT '10' COLLATE utf8_general_ci XOR '20' COLLATE utf8_unicode_ci;
 
+--echo #
+--echo # MDEV-8705 Wrong result for SELECT..WHERE latin1_bin_column='a' AND latin1_bin_column='A'
+--echo #
+SET NAMES utf8 COLLATE utf8_german2_ci;
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET utf8 COLLATE utf8_bin);
+INSERT INTO t1 VALUES ('a'),('A');
+SELECT * FROM t1 WHERE a='a';
+SELECT * FROM t1 WHERE a=_utf8'a';
+# Make sure this does not return "Illegal mix of collations"
+SELECT * FROM t1 WHERE a='a' AND a=_utf8'a';
+DROP TABLE t1;
+SET NAMES utf8;
 
 --echo #
 --echo # End of MariaDB-10.1 tests

sql/item_cmpfunc.cc

@@ -5920,7 +5920,7 @@ Item_equal::Item_equal(THD *thd, Item *f1, Item *f2, bool with_const_item):
   with_const= with_const_item;
   equal_items.push_back(f1, thd->mem_root);
   equal_items.push_back(f2, thd->mem_root);
-  compare_as_dates= with_const_item && f2->cmp_type() == TIME_RESULT;
+  cmp.cmp_collation.set(f2->collation);
   cmp.set_compare_type(item_cmp_type(f1, f2));
   upper_levels= NULL;
 }
@@ -5950,7 +5950,7 @@ Item_equal::Item_equal(THD *thd, Item_equal *item_equal):
     equal_items.push_back(item, thd->mem_root);
   }
   with_const= item_equal->with_const;
-  compare_as_dates= item_equal->compare_as_dates;
+  cmp.cmp_collation.set(item_equal->cmp.cmp_collation);
   cmp.set_compare_type(item_equal->cmp.compare_type());
   cond_false= item_equal->cond_false;
   upper_levels= item_equal->upper_levels;
@@ -5971,41 +5971,85 @@ Item_equal::Item_equal(THD *thd, Item_equal *item_equal):
   the list. Otherwise the value of c is compared with the value of the
   constant item from equal_items. If they are not equal cond_false is set
   to TRUE. This serves as an indicator that this Item_equal is always FALSE.
-  The optional parameter f is used to adjust the flag compare_as_dates.
 */
 
-void Item_equal::add_const(THD *thd, Item *c, Item *f)
+void Item_equal::add_const(THD *thd, Item *c)
 {
   if (cond_false)
     return;
   if (!with_const)
   {
     with_const= TRUE;
-    if (f)
-      compare_as_dates= f->cmp_type() == TIME_RESULT;
     equal_items.push_front(c, thd->mem_root);
     return;
   }
   Item *const_item= get_const();
-  if (compare_as_dates)
-  {
-    cmp.set_datetime_cmp_func(this, &c, &const_item);
-    cond_false= cmp.compare();
-  }
-  else
-  {
-    Item_func_eq *func= new (thd->mem_root) Item_func_eq(thd, c, const_item);
-    if (func->set_cmp_func())
+  switch (cmp.compare_type()) {
+  case TIME_RESULT:
     {
+      cmp.set_datetime_cmp_func(this, &c, &const_item);
+      cond_false= cmp.compare();
+      break;
+    }
+  case STRING_RESULT:
+    {
+      String *str1, *str2;
       /*
-        Setting a comparison function fails when trying to compare
-        incompatible charsets. Charset compatibility is checked earlier,
-        except for constant subqueries where we may do it here.
+        Suppose we have an expression (with a string type field) like this:
+          WHERE field=const1 AND field=const2 ...
+
+        For all pairs field=constXXX we know that:
+
+        - Item_func_eq::fix_length_and_dec() performed collation and character
+        set aggregation and added character set converters when needed.
+        Note, the case like:
+          WHERE field=const1 COLLATE latin1_bin AND field=const2
+        is not handled here, because the field would be replaced to
+        Item_func_set_collation, which cannot get into Item_equal.
+        So all constXXX that are handled by Item_equal
+        already have compatible character sets with "field".
+
+        - Also, Field_str::test_if_equality_guarantees_uniqueness() guarantees
+        that the comparison collation of all equalities handled by Item_equal
+        match the the collation of the field.
+
+        Therefore, at Item_equal::add_const() time all constants constXXX
+        should be directly comparable to each other without an additional
+        character set conversion.
+        It's safe to do val_str() for "const_item" and "c" and compare
+        them according to the collation of the *field*.
+
+        So in a script like this:
+          CREATE TABLE t1 (a VARCHAR(10) COLLATE xxx);
+          INSERT INTO t1 VALUES ('a'),('A');
+          SELECT * FROM t1 WHERE a='a' AND a='A';
+        Item_equal::add_const() effectively rewrites the condition to:
+          SELECT * FROM t1 WHERE a='a' AND 'a' COLLATE xxx='A';
+        and then to:
+          SELECT * FROM t1 WHERE a='a'; // if the two constants were equal
+                                        // e.g. in case of latin1_swedish_ci
+        or to:
+          SELECT * FROM t1 WHERE FALSE; // if the two constants were not equal
+                                        // e.g. in case of latin1_bin
+
+        Note, both "const_item" and "c" can return NULL, e.g.:
+          SELECT * FROM t1 WHERE a=NULL    AND a='const';
+          SELECT * FROM t1 WHERE a='const' AND a=NULL;
+          SELECT * FROM t1 WHERE a='const' AND a=(SELECT MAX(a) FROM t2)
       */
-      return;
+      cond_false= !(str1= const_item->val_str(&cmp.value1)) ||
+                  !(str2= c->val_str(&cmp.value2)) ||
+                  !str1->eq(str2, compare_collation());
+      break;
+    }
+  default:
+    {
+      Item_func_eq *func= new (thd->mem_root) Item_func_eq(thd, c, const_item);
+      if (func->set_cmp_func())
+        return;
+      func->quick_fix_field();
+      cond_false= !func->val_int();
     }
-    func->quick_fix_field();
-    cond_false= !func->val_int();
   }
   if (with_const && equal_items.elements == 1)
     cond_true= TRUE;
@@ -6482,14 +6526,6 @@ void Item_equal::print(String *str, enum_query_type query_type)
 }
 
 
-CHARSET_INFO *Item_equal::compare_collation() const
-{ 
-  Item_equal_fields_iterator it(*((Item_equal*) this));
-  Item *item= it++;
-  return item->collation.collation;
-}
-
-
 /*
   @brief Get the first equal field of multiple equality.
   @param[in] field   the field to get equal field to

sql/item_cmpfunc.h

@@ -2052,12 +2052,6 @@ class Item_equal: public Item_bool_func
     the equal_items should be ignored.
   */
   bool cond_true;
-  /* 
-    compare_as_dates=TRUE <-> constants equal to fields from equal_items
-    must be compared as datetimes and not as strings.
-    compare_as_dates can be TRUE only if with_const=TRUE 
-  */
-  bool compare_as_dates;
   /* 
     The comparator used to compare constants equal to fields from equal_items
     as datetimes. The comparator is used only if compare_as_dates=TRUE
@@ -2080,7 +2074,7 @@ public:
   Item_equal(THD *thd, Item_equal *item_equal);
   /* Currently the const item is always the first in the list of equal items */
   inline Item* get_const() { return with_const ? equal_items.head() : NULL; }
-  void add_const(THD *thd, Item *c, Item *f = NULL);
+  void add_const(THD *thd, Item *c);
   /** Add a non-constant item to the multiple equality */
   void add(Item *f, MEM_ROOT *root) { equal_items.push_back(f, root); }
   bool contains(Field *field);
@@ -2110,7 +2104,8 @@ public:
   Item *transform(THD *thd, Item_transformer transformer, uchar *arg);
   virtual void print(String *str, enum_query_type query_type);
   Item_result compare_type() const { return cmp.compare_type(); }
-  CHARSET_INFO *compare_collation() const;
+  CHARSET_INFO *compare_collation() const
+  { return cmp.cmp_collation.collation; }
 
   void set_context_field(Item_field *ctx_field) { context_field= ctx_field; }
   void set_link_equal_fields(bool flag) { link_equal_fields= flag; }

sql/sql_select.cc

@@ -12699,7 +12699,7 @@ static bool check_simple_equality(THD *thd, const Item::Context &ctx,
           already contains a constant and its value is  not equal to
           the value of const_item.
         */
-        item_equal->add_const(thd, const_item2, orig_field_item);
+        item_equal->add_const(thd, const_item2);
       }
       else
       {