MDEV-10865 COLLATE keyword doesn't work in PREPARE query

Fixing applying the COLLATE clause to a parameter caused an error error:
  COLLATION '...' is not valid for CHARACTER SET 'binary'

Fix:

- Changing the collation derivation for a non-prepared Item_param
  to DERIVATION_IGNORABLE.

- Allowing to apply any COLLATE clause to expressions with DERIVATION_IGNORABLE.
  This includes:
    1. A non-prepared Item_param
    2. An explicit NULL
    3. Expressions derived from #1 and #2

  For example:
    SELECT ? COLLATE utf8mb_unicode_ci;
    SELECT NULL COLLATE utf8mb_unicode_ci;
    SELECT CONCAT(?) COLLATE utf8mb_unicode_ci;
    SELECT CONCAT(NULL) COLLATE utf8mb_unicode_ci

- Additional change: preserving the collation of an expression when
  the expression gets assigned to a PS parameter and evaluates to SQL NULL.
  Before this change, the collation of the parameter was erroneously set
  to &my_charset_binary.

- Additional change: removing the multiplication to mbmaxlen from the
  fix_char_length_ulonglong() argument, because the multiplication already
  happens inside fix_char_length_ulonglong().
  This fixes a too large column size created for a COLLATE clause.

mysql-test/main/ctype_collate_context.result

@@ -3716,3 +3716,103 @@ DROP PROCEDURE p;
 #
 # End of 10.9 tests
 #
+#
+# Start of 10.11 tests
+#
+#
+# MDEV-10865 COLLATE keyword doesn't work in PREPARE query
+#
+SET NAMES utf8mb4;
+#
+# A context collation and an explicit NULL
+#
+SELECT NULL COLLATE uca1400_ai_ci;
+ERROR HY000: 'NULL' is not allowed in this context
+SELECT CONCAT(NULL) COLLATE uca1400_ai_ci;
+ERROR HY000: 'NULL' is not allowed in this context
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT NULL COLLATE uca1400_ai_ci AS c1';
+ERROR HY000: 'NULL' is not allowed in this context
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT CONCAT(NULL) COLLATE uca1400_ai_ci AS c1';
+ERROR HY000: 'NULL' is not allowed in this context
+#
+# A context collation and a parameter bound to NULL
+#
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING NULL;
+ERROR HY000: 'NULL' is not allowed in this context
+EXECUTE stmt USING CONCAT(NULL);
+ERROR HY000: 'NULL' is not allowed in this context
+EXECUTE stmt USING NULL COLLATE uca1400_ai_ci;
+ERROR HY000: 'NULL' is not allowed in this context
+EXECUTE stmt USING CONCAT(NULL) COLLATE uca1400_ai_ci;
+ERROR HY000: 'NULL' is not allowed in this context
+#
+# A context collation and CONVERT(NULL USING ...)
+#
+EXECUTE stmt USING CONVERT(NULL USING utf8mb4);
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` char(0) CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+EXECUTE stmt USING CONVERT(NULL USING utf8mb4) COLLATE uca1400_ai_ci;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` char(0) CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+EXECUTE stmt USING CONVERT(NULL USING binary);
+ERROR 42000: COLLATION 'uca1400_ai_ci' is not valid for CHARACTER SET 'binary'
+EXECUTE stmt USING CONVERT(NULL USING latin1);
+ERROR 42000: COLLATION 'uca1400_ai_ci' is not valid for CHARACTER SET 'latin1'
+#
+# A context collation and an expression with a parameter
+# whose character does not get resolved when bound to a not-NULL value
+#
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT LEFT(NULL,?) COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING NULL;
+ERROR HY000: 'NULL' is not allowed in this context
+#
+# A context collation and an expression with a parameter
+# whose character set gets resolved when bound to a not-NULL value
+#
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING 1;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` varchar(1) CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING _binary'test';
+ERROR 42000: COLLATION 'uca1400_ai_ci' is not valid for CHARACTER SET 'binary'
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` varchar(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING 'test' COLLATE utf8mb4_bin;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` varchar(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING _latin1'test' COLLATE latin1_bin;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` varchar(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+#
+# End of 10.11 tests
+#

mysql-test/main/ctype_collate_context.test

@@ -401,3 +401,103 @@ DROP PROCEDURE p;
 --echo #
 --echo # End of 10.9 tests
 --echo #
+
+--echo #
+--echo # Start of 10.11 tests
+--echo #
+
+--echo #
+--echo # MDEV-10865 COLLATE keyword doesn't work in PREPARE query
+--echo #
+
+SET NAMES utf8mb4;
+
+--echo #
+--echo # A context collation and an explicit NULL
+--echo #
+
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+SELECT NULL COLLATE uca1400_ai_ci;
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+SELECT CONCAT(NULL) COLLATE uca1400_ai_ci;
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT NULL COLLATE uca1400_ai_ci AS c1';
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT CONCAT(NULL) COLLATE uca1400_ai_ci AS c1';
+
+
+--echo #
+--echo # A context collation and a parameter bound to NULL
+--echo #
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+EXECUTE stmt USING NULL;
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+EXECUTE stmt USING CONCAT(NULL);
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+EXECUTE stmt USING NULL COLLATE uca1400_ai_ci;
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+EXECUTE stmt USING CONCAT(NULL) COLLATE uca1400_ai_ci;
+
+--echo #
+--echo # A context collation and CONVERT(NULL USING ...)
+--echo #
+
+EXECUTE stmt USING CONVERT(NULL USING utf8mb4);
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+EXECUTE stmt USING CONVERT(NULL USING utf8mb4) COLLATE uca1400_ai_ci;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+--error ER_COLLATION_CHARSET_MISMATCH
+EXECUTE stmt USING CONVERT(NULL USING binary);
+
+--error ER_COLLATION_CHARSET_MISMATCH
+EXECUTE stmt USING CONVERT(NULL USING latin1);
+
+--echo #
+--echo # A context collation and an expression with a parameter
+--echo # whose character does not get resolved when bound to a not-NULL value
+--echo #
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT LEFT(NULL,?) COLLATE uca1400_ai_ci AS c1';
+--error ER_NOT_ALLOWED_IN_THIS_CONTEXT
+EXECUTE stmt USING NULL;
+
+
+--echo #
+--echo # A context collation and an expression with a parameter
+--echo # whose character set gets resolved when bound to a not-NULL value
+--echo #
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING 1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+--error ER_COLLATION_CHARSET_MISMATCH
+EXECUTE stmt USING _binary'test';
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING 'test' COLLATE utf8mb4_bin;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE uca1400_ai_ci AS c1';
+EXECUTE stmt USING _latin1'test' COLLATE latin1_bin;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+
+--echo #
+--echo # End of 10.11 tests
+--echo #

mysql-test/main/ctype_utf32.result

@@ -3024,3 +3024,88 @@ HEX(DATE_FORMAT(TIME'11:22:33',@format))
 #
 # End of 10.4 tests
 #
+#
+# Start of 10.11 tests
+#
+#
+# MDEV-10865 COLLATE keyword doesn't work in PREPARE query
+#
+#
+# The collation is not applicable to the PS parameter
+#
+SET NAMES utf8mb4;
+CREATE TABLE t1 (
+c1 varchar(500) COLLATE utf32_unicode_ci NOT NULL
+);
+INSERT INTO t1 VALUES ('jj');
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE c1 LIKE ? COLLATE utf32_unicode_ci';
+EXECUTE stmt USING 'jj';
+ERROR 42000: COLLATION 'utf32_unicode_ci' is not valid for CHARACTER SET 'utf8mb4'
+DROP TABLE t1;
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE utf32_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+ERROR 42000: COLLATION 'utf32_unicode_ci' is not valid for CHARACTER SET 'utf8mb4'
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT CONCAT(?) COLLATE utf32_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+ERROR 42000: COLLATION 'utf32_unicode_ci' is not valid for CHARACTER SET 'utf8mb4'
+CREATE TABLE t1 AS SELECT NULL COLLATE utf32_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` char(0) CHARACTER SET utf32 COLLATE utf32_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+CREATE TABLE t1 AS SELECT CONCAT(NULL) COLLATE utf32_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` char(0) CHARACTER SET utf32 COLLATE utf32_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+#
+# The collation is applicable to the PS parameter
+#
+SET NAMES utf8mb4, collation_connection=utf32_general_ci;
+CREATE TABLE t1 (
+c1 varchar(500) COLLATE utf32_unicode_ci NOT NULL
+);
+INSERT INTO t1 VALUES ('jj');
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE c1 LIKE ? COLLATE utf32_unicode_ci';
+EXECUTE stmt USING 'jj';
+c1
+jj
+DROP TABLE t1;
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE utf32_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` varchar(4) CHARACTER SET utf32 COLLATE utf32_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT CONCAT(?) COLLATE utf32_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` varchar(4) CHARACTER SET utf32 COLLATE utf32_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+CREATE TABLE t1 AS SELECT NULL COLLATE utf32_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` char(0) CHARACTER SET utf32 COLLATE utf32_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+CREATE TABLE t1 AS SELECT CONCAT(NULL) COLLATE utf32_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` char(0) CHARACTER SET utf32 COLLATE utf32_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+SET NAMES utf8mb4;
+#
+# End of 10.11 tests
+#

mysql-test/main/ctype_utf32.test

@@ -1167,4 +1167,80 @@ SELECT HEX(DATE_FORMAT(TIME'11:22:33',@format));
 --echo # End of 10.4 tests
 --echo #
 
+--echo #
+--echo # Start of 10.11 tests
+--echo #
+
+--echo #
+--echo # MDEV-10865 COLLATE keyword doesn't work in PREPARE query
+--echo #
+
+--echo #
+--echo # The collation is not applicable to the PS parameter
+--echo #
+
+SET NAMES utf8mb4;
+CREATE TABLE t1 (
+   c1 varchar(500) COLLATE utf32_unicode_ci NOT NULL
+);
+INSERT INTO t1 VALUES ('jj');
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE c1 LIKE ? COLLATE utf32_unicode_ci';
+--error ER_COLLATION_CHARSET_MISMATCH
+EXECUTE stmt USING 'jj';
+DROP TABLE t1;
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE utf32_unicode_ci AS c1';
+--error ER_COLLATION_CHARSET_MISMATCH
+EXECUTE stmt USING 'test';
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT CONCAT(?) COLLATE utf32_unicode_ci AS c1';
+--error ER_COLLATION_CHARSET_MISMATCH
+EXECUTE stmt USING 'test';
+
+CREATE TABLE t1 AS SELECT NULL COLLATE utf32_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 AS SELECT CONCAT(NULL) COLLATE utf32_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+
+--echo #
+--echo # The collation is applicable to the PS parameter
+--echo #
+
+SET NAMES utf8mb4, collation_connection=utf32_general_ci;
+CREATE TABLE t1 (
+   c1 varchar(500) COLLATE utf32_unicode_ci NOT NULL
+);
+INSERT INTO t1 VALUES ('jj');
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE c1 LIKE ? COLLATE utf32_unicode_ci';
+EXECUTE stmt USING 'jj';
+DROP TABLE t1;
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE utf32_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT CONCAT(?) COLLATE utf32_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 AS SELECT NULL COLLATE utf32_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 AS SELECT CONCAT(NULL) COLLATE utf32_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+SET NAMES utf8mb4;
+
+--echo #
+--echo # End of 10.11 tests
+--echo #
+
 --enable_service_connection

mysql-test/main/ctype_utf8mb4.result

@@ -4182,24 +4182,6 @@ DROP TABLE t1;
 # End of 10.2 tests
 #
 #
-# Start of 10.5 tests
-#
-#
-# MDEV-24584 Selecting INT column with COLLATE utf8mb4_general_ci throws an error
-#
-SET NAMES utf8mb4;
-SELECT 1 COLLATE utf8mb4_general_ci;
-1 COLLATE utf8mb4_general_ci
-1
-SELECT 1 COLLATE utf8mb4_bin;
-1 COLLATE utf8mb4_bin
-1
-SELECT 1 COLLATE latin1_swedish_ci;
-ERROR 42000: COLLATION 'latin1_swedish_ci' is not valid for CHARACTER SET 'utf8mb4'
-#
-# End of 10.5 tests
-#
-#
 # Start of 10.6 tests
 #
 #
@@ -4227,3 +4209,67 @@ DROP TABLE t1;
 #
 # End of 10.6 tests
 #
+#
+# Start of 10.11 tests
+#
+#
+# MDEV-24584 Selecting INT column with COLLATE utf8mb4_general_ci throws an error
+#
+SET NAMES utf8mb4;
+SELECT 1 COLLATE utf8mb4_general_ci;
+1 COLLATE utf8mb4_general_ci
+1
+SELECT 1 COLLATE utf8mb4_bin;
+1 COLLATE utf8mb4_bin
+1
+SELECT 1 COLLATE latin1_swedish_ci;
+ERROR 42000: COLLATION 'latin1_swedish_ci' is not valid for CHARACTER SET 'utf8mb4'
+#
+# MDEV-10865 COLLATE keyword doesn't work in PREPARE query
+#
+SET NAMES utf8mb4;
+CREATE TABLE t1 (
+c1 varchar(500) COLLATE utf8mb4_unicode_ci NOT NULL
+) CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+INSERT INTO t1 VALUES ('jj');
+SELECT * FROM t1 WHERE c1 LIKE 'jj' COLLATE utf8mb4_unicode_ci;
+c1
+jj
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE c1 LIKE ? COLLATE utf8mb4_unicode_ci';
+EXECUTE stmt USING 'jj';
+c1
+jj
+DROP TABLE t1;
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE utf8mb4_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` varchar(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT CONCAT(?) COLLATE utf8mb4_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` varchar(4) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+CREATE TABLE t1 AS SELECT NULL COLLATE utf8mb4_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` char(0) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+CREATE TABLE t1 AS SELECT CONCAT(NULL) COLLATE utf8mb4_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` char(0) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t1;
+#
+# End of 10.11 tests
+#

mysql-test/main/ctype_utf8mb4.test

@@ -2068,25 +2068,6 @@ DROP TABLE t1;
 --echo # End of 10.2 tests
 --echo #
 
-
---echo #
---echo # Start of 10.5 tests
---echo #
-
---echo #
---echo # MDEV-24584 Selecting INT column with COLLATE utf8mb4_general_ci throws an error
---echo #
-
-SET NAMES utf8mb4;
-SELECT 1 COLLATE utf8mb4_general_ci;
-SELECT 1 COLLATE utf8mb4_bin;
---error ER_COLLATION_CHARSET_MISMATCH
-SELECT 1 COLLATE latin1_swedish_ci;
-
---echo #
---echo # End of 10.5 tests
---echo #
-
 --echo #
 --echo # Start of 10.6 tests
 --echo #
@@ -2112,3 +2093,55 @@ DROP TABLE t1;
 --echo #
 --echo # End of 10.6 tests
 --echo #
+
+
+--echo #
+--echo # Start of 10.11 tests
+--echo #
+
+--echo #
+--echo # MDEV-24584 Selecting INT column with COLLATE utf8mb4_general_ci throws an error
+--echo #
+
+SET NAMES utf8mb4;
+SELECT 1 COLLATE utf8mb4_general_ci;
+SELECT 1 COLLATE utf8mb4_bin;
+--error ER_COLLATION_CHARSET_MISMATCH
+SELECT 1 COLLATE latin1_swedish_ci;
+
+--echo #
+--echo # MDEV-10865 COLLATE keyword doesn't work in PREPARE query
+--echo #
+
+SET NAMES utf8mb4;
+CREATE TABLE t1 (
+   c1 varchar(500) COLLATE utf8mb4_unicode_ci NOT NULL
+) CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+INSERT INTO t1 VALUES ('jj');
+SELECT * FROM t1 WHERE c1 LIKE 'jj' COLLATE utf8mb4_unicode_ci;
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE c1 LIKE ? COLLATE utf8mb4_unicode_ci';
+EXECUTE stmt USING 'jj';
+DROP TABLE t1;
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT ? COLLATE utf8mb4_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+PREPARE stmt FROM 'CREATE TABLE t1 AS SELECT CONCAT(?) COLLATE utf8mb4_unicode_ci AS c1';
+EXECUTE stmt USING 'test';
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 AS SELECT NULL COLLATE utf8mb4_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 AS SELECT CONCAT(NULL) COLLATE utf8mb4_unicode_ci AS c1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+
+--echo #
+--echo # End of 10.11 tests
+--echo #

sql/item.cc

@@ -4119,6 +4119,7 @@ Item_param::Item_param(THD *thd, const LEX_CSTRING *name_arg,
   */
   set_maybe_null();
   with_flags= with_flags | item_with_t::PARAM;
+  collation= DTCollation(&my_charset_bin, DERIVATION_IGNORABLE);
 }
 
 
@@ -4174,7 +4175,7 @@ void Item_param::sync_clones()
 }
 
 
-void Item_param::set_null()
+void Item_param::set_null(const DTCollation &c)
 {
   DBUG_ENTER("Item_param::set_null");
   /*
@@ -4189,6 +4190,7 @@ void Item_param::set_null()
   */
   max_length= 0;
   decimals= 0;
+  collation= c;
   state= NULL_VALUE;
   DBUG_VOID_RETURN;
 }
@@ -4447,7 +4449,7 @@ bool Item_param::set_from_item(THD *thd, Item *item)
     longlong val= item->val_int();
     if (item->null_value)
     {
-      set_null();
+      set_null(DTCollation_numeric());
       DBUG_RETURN(false);
     }
     else
@@ -4465,7 +4467,7 @@ bool Item_param::set_from_item(THD *thd, Item *item)
     DBUG_RETURN(set_value(thd, item, &tmp, h));
   }
   else
-    set_null();
+    set_null_string(item->collation);
 
   DBUG_RETURN(0);
 }
@@ -5048,7 +5050,7 @@ Item_param::set_value(THD *thd, sp_rcontext *ctx, Item **it)
   if (arg->save_in_value(thd, &tmp) ||
       set_value(thd, arg, &tmp, arg->type_handler()))
   {
-    set_null();
+    set_null_string(arg->collation);
     return false;
   }
   /* It is wrapper => other set_* shoud set null_value */

sql/item.h

@@ -4234,7 +4234,32 @@ class Item_param :public Item_basic_value,
 
   void set_default();
   void set_ignore();
-  void set_null();
+  void set_null(const DTCollation &c);
+  void set_null_string(const DTCollation &c)
+  {
+    /*
+      We need to distinguish explicit NULL (marked by DERIVATION_IGNORABLE)
+      from other item types:
+
+      - These statements should give an error, because
+        the character set of the bound parameter is not known:
+          EXECUTE IMMEDIATE "SELECT ? COLLATE utf8mb4_bin" USING NULL;
+          EXECUTE IMMEDIATE "SELECT ? COLLATE utf8mb4_bin" USING CONCAT(NULL);
+
+      - These statements should return a good result, because
+        the character set of the bound parameter is known:
+          EXECUTE IMMEDIATE "SELECT ? COLLATE utf8mb4_bin"
+                      USING CONVERT(NULL USING utf8mb4);
+          EXECUTE IMMEDIATE "SELECT ? COLLATE utf8mb4_bin"
+                      USING CAST(NULL AS CHAR CHARACTER SET utf8mb4);
+    */
+    set_null(DTCollation(c.collation, MY_MAX(c.derivation,
+                                             DERIVATION_COERCIBLE)));
+  }
+  void set_null()
+  {
+    set_null(DTCollation(&my_charset_bin, DERIVATION_IGNORABLE));
+  }
   void set_int(longlong i, uint32 max_length_arg);
   void set_double(double i);
   void set_decimal(const char *str, ulong length);

sql/item_strfunc.cc

@@ -3880,21 +3880,43 @@ String *Item_func_set_collation::val_str(String *str)
   str=args[0]->val_str(str);
   if ((null_value=args[0]->null_value))
     return 0;
+  /*
+    Let SCS be the character set of the source - args[0].
+    Let TCS be the character set of the target - i.e. the character set
+    of the collation specified in the COLLATE clause.
+
+    It's OK to return SQL NULL if SCS is not equal to TCS.
+    This is possible on the explicit NULL or expressions derived from
+    the explicit NULL:
+      SELECT NULL COLLATE utf8mb4_general_ci;
+      SELECT COALESCE(NULL) COLLATE utf8mb4_general_ci;
+
+    But for a non-NULL result SCS and TCS must be compatible:
+    1. Either SCS==TCS
+    2. Or SCS can be can be reinterpeted to TCS.
+       This scenario is possible when args[0] is numeric and TCS->mbmaxlen==1.
+
+    If SCS and TCS are not compatible here, then something went wrong during
+    fix_fields(), e.g. an Item_func_conv_charset was not added two wrap args[0].
+  */
+  DBUG_ASSERT(my_charset_same(args[0]->collation.collation,
+                              collation.collation) ||
+              (args[0]->collation.repertoire == MY_REPERTOIRE_ASCII &&
+               !(collation.collation->state & MY_CS_NONASCII)));
   str->set_charset(collation.collation);
   return str;
 }
 
 bool Item_func_set_collation::fix_length_and_dec(THD *thd)
 {
-  if (agg_arg_charsets_for_string_result(collation, args, 1))
-    return true;
-  Lex_exact_charset_opt_extended_collate cl(collation.collation, true);
-  if (cl.merge_collation_override(m_set_collation))
+  if (agg_arg_charsets_for_string_result(collation, args, 1) ||
+      collation.merge_collation(m_set_collation,
+                                args[0]->collation.repertoire,
+                                with_param() &&
+                                thd->lex->is_ps_or_view_context_analysis()))
     return true;
-  collation.set(cl.collation().charset_info(), DERIVATION_EXPLICIT,
-                args[0]->collation.repertoire);
   ulonglong max_char_length= (ulonglong) args[0]->max_char_length();
-  fix_char_length_ulonglong(max_char_length * collation.collation->mbmaxlen);
+  fix_char_length_ulonglong(max_char_length);
 
   return FALSE;
 }

sql/sql_type.cc

@@ -33,6 +33,88 @@ const DTCollation &DTCollation_numeric::singleton()
   return tmp;
 }
 
+
+bool
+DTCollation::merge_charset_and_collation(CHARSET_INFO *cs,
+                                         const Lex_extended_collation_st &cl,
+                                         my_repertoire_t repertoire)
+{
+  Lex_exact_charset_opt_extended_collate cscl(cs, true);
+  if (cscl.merge_collation_override(cl))
+    return true;
+  set(cscl.collation().charset_info(), DERIVATION_EXPLICIT, repertoire);
+  return false;
+}
+
+
+bool DTCollation::merge_collation(const Lex_extended_collation_st &cl,
+                                  my_repertoire_t repertoire,
+                                  bool allow_ignorable_with_context_collation)
+{
+  if (derivation != DERIVATION_IGNORABLE)
+  {
+    // A known character set + an extended collation
+    return merge_charset_and_collation(collation, cl, repertoire);
+  }
+
+  if (cl.type() == Lex_extended_collation::TYPE_EXACT)
+  {
+    /*
+      An unknown character set + an exact collation.
+      Just use this exact collation.
+      Examples:
+      - Expressions derived from an explicit NULL:
+          SELECT NULL         COLLATE utf8mb4_general_ci;
+          SELECT CONCAT(NULL) COLLATE utf8mb4_general_ci;
+        Any collation is applicable to an explicit NULL.
+
+      - Expressions with PS parameters (at PREPARE time, not bound yet)
+          SELECT ?         COLLATE utf8mb4_general_ci;
+          SELECT CONCAT(?) COLLATE utf8mb4_general_ci;
+        The collation will be checked for applicability to the
+        character set of the actual bound parameter at the EXECUTE time.
+        We're now in PREPARE: let's assume it will be applicable.
+    */
+    set(cl.charset_info(), DERIVATION_EXPLICIT, repertoire);
+    return false;
+  }
+
+  // An unknown character set + a contextually typed collation
+  if (allow_ignorable_with_context_collation)
+  {
+    /*
+      Expressions with non-bound PS parameters, PREPARE time.
+        SELECT ?         COLLATE uca1400_ai_ci;
+        SELECT CONCAT(?) COLLATE uca1400_ai_ci;
+      There is a chance the character set of the actual bound parameter
+      will be known at the EXECUTE time (unless an explicit NULL is bound).
+
+      For now let's use utf8mb4 to resolve collations like uca1400_ai_ci.
+      The real character set of the actual bound parameter expression will be
+      later used to resolve the collation again, during the EXECUTE time.
+    */
+    return merge_charset_and_collation(&my_charset_utf8mb4_general_ci,
+                                       cl, repertoire);
+  }
+
+  /*
+    Expressions with an unknown character set:
+    - Either without PS parameters at all:
+        SELECT NULL         COLLATE uca1400_ai_ci;
+        SELECT CONCAT(NULL) COLLATE uca1400_ai_ci;
+    - Or with PS parameters bound to NULL at EXECUTE time:
+        EXECUTE IMMEDIATE
+          'SELECT ? COLLATE uca1400_ai_ci' USING NULL;
+        EXECUTE IMMEDIATE
+          'SELECT CONCAT(?) COLLATE uca1400_ai_ci' USING NULL;
+        EXECUTE IMMEDIATE
+          'SELECT ? COLLATE uca1400_ai_ci' USING CONCAT(NULL);
+  */
+  my_error(ER_NOT_ALLOWED_IN_THIS_CONTEXT, MYF(0), "NULL");
+  return true;
+}
+
+
 Named_type_handler<Type_handler_row> type_handler_row("row");
 
 Named_type_handler<Type_handler_null> type_handler_null("null");

sql/sql_type.h

@@ -3076,6 +3076,12 @@ class DTCollation {
   bool aggregate(const DTCollation &dt, uint flags= 0);
   bool set(DTCollation &dt1, DTCollation &dt2, uint flags= 0)
   { set(dt1); return aggregate(dt2, flags); }
+  bool merge_charset_and_collation(CHARSET_INFO *cs,
+                                   const Lex_extended_collation_st &cl,
+                                   my_repertoire_t repertoire);
+  bool merge_collation(const Lex_extended_collation_st &cl,
+                       my_repertoire_t repertoire,
+                       bool allow_ignorable_with_context_collation);
   const char *derivation_name() const
   {
     switch(derivation)