MDEV-13358: FIRST_V throw SQL Fehler (1292): Incorrect datetime value

This is backport of 25ad623d for 10.2.

The issue is similar to the one from MDEV-13240. Item::save_in_field()
returns an error during tmp table population in a create table from select query
as we try to save an empty string as a date value when
force_return_blank is set to true for window functions.

    MDEV-13240 Wrong warning with MAX(datetime_field) OVER (...)

    The problem resided in Item_window_func implementation,
    and it was revealed by bb-10.2-ext specific changes:

    Item_window_func::save_in_field() works differently in bb-10.2-ext vs 10.2:

    - 10.2 goes through val_str()
    - bb-10.2-ext goes through get_date(), due to Type_handler related changes.
      get_date() tries to convert empty string to DATETIME, hence the warning.

    During a discussion with Vicentiu, it was decided to fix
    Item_window_func::val_xxx() to return NULL
    (instead of an "empty" value, such as 0 for numbers and '' for strings)
    when force_return_blank is set.

mysql-test/r/win.result

@@ -3185,3 +3185,32 @@ fld
 1
 2
 DROP TABLE t1;
+#
+# MDEV-13240 Wrong warning with MAX(datetime_field) OVER (...)
+#
+CREATE TABLE t1 (dt DATETIME);
+INSERT INTO t1 VALUES ('2017-05-17');
+SELECT MAX(dt) OVER (ORDER BY dt ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING) FROM t1;
+MAX(dt) OVER (ORDER BY dt ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING)
+NULL
+DROP TABLE t1;
+#
+# MDEV-13358 FIRST_VALUE throws SQL Error (1292): Incorrect datetime value
+#
+CREATE TABLE IF NOT EXISTS `fv_test` (
+`SOME_DATE` datetime NOT NULL
+);
+INSERT INTO `fv_test` (`SOME_DATE`) VALUES ('2017-07-20 12:47:56');
+CREATE TABLE fv_result
+SELECT
+FIRST_VALUE(SOME_DATE) OVER(ORDER BY SOME_DATE DESC) AS somedate
+FROM fv_test;
+SHOW CREATE TABLE fv_result;
+Table	Create Table
+fv_result	CREATE TABLE `fv_result` (
+  `somedate` datetime DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+SELECT * FROM fv_result;
+somedate
+2017-07-20 12:47:56
+DROP TABLE fv_test, fv_result;

mysql-test/r/win_insert_select.result

 CREATE TABLE t1 (c1 INT, c2 VARCHAR(30));
 PREPARE populate_table FROM "INSERT into t1 values (1, 'manual_insert_1'),
                                                    (4, 'manual_insert_2')";
-INSERT INTO t1 SELECT row_number() over(), "should_have_0" FROM t1;
-INSERT INTO t1 SELECT 1 + row_number() over(), "should_have_2" FROM t1;
+INSERT INTO t1 SELECT row_number() over(), "should_not_add_any_rows" FROM t1;
+INSERT INTO t1 SELECT 1 + row_number() over(), "should_not_add_any_rows" FROM t1;
 EXECUTE populate_table;
-INSERT INTO t1 SELECT 10 + row_number() over(), "should repeat 4 times [11-14]" FROM t1;
+INSERT INTO t1 SELECT 10 + row_number() over(), "should repeat 2 times [11-12]" FROM t1;
 SELECT c1, c2 FROM t1 ORDER BY c2, c1;
 c1	c2
 1	manual_insert_1
 4	manual_insert_2
-11	should repeat 4 times [11-14]
-12	should repeat 4 times [11-14]
+11	should repeat 2 times [11-12]
+12	should repeat 2 times [11-12]
 DELETE FROM t1;
 EXECUTE populate_table;
 INSERT INTO t1

mysql-test/t/win.test

@@ -1965,3 +1965,31 @@ INSERT INTO t1 VALUES (1),(2);
 SELECT i AS fld FROM t1 UNION SELECT COUNT(*) AS fld FROM t1;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-13240 Wrong warning with MAX(datetime_field) OVER (...)
+--echo #
+
+CREATE TABLE t1 (dt DATETIME);
+INSERT INTO t1 VALUES ('2017-05-17');
+SELECT MAX(dt) OVER (ORDER BY dt ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING) FROM t1;
+DROP TABLE t1;
+
+--echo #
+--echo # MDEV-13358 FIRST_VALUE throws SQL Error (1292): Incorrect datetime value
+--echo #
+CREATE TABLE IF NOT EXISTS `fv_test` (
+        `SOME_DATE` datetime NOT NULL
+        );
+
+INSERT INTO `fv_test` (`SOME_DATE`) VALUES ('2017-07-20 12:47:56');
+
+CREATE TABLE fv_result
+SELECT
+FIRST_VALUE(SOME_DATE) OVER(ORDER BY SOME_DATE DESC) AS somedate
+FROM fv_test;
+
+SHOW CREATE TABLE fv_result;
+
+SELECT * FROM fv_result;
+
+DROP TABLE fv_test, fv_result;

mysql-test/t/win_insert_select.test

@@ -3,12 +3,12 @@ CREATE TABLE t1 (c1 INT, c2 VARCHAR(30));
 PREPARE populate_table FROM "INSERT into t1 values (1, 'manual_insert_1'),
                                                    (4, 'manual_insert_2')";
 
-INSERT INTO t1 SELECT row_number() over(), "should_have_0" FROM t1;
-INSERT INTO t1 SELECT 1 + row_number() over(), "should_have_2" FROM t1;
+INSERT INTO t1 SELECT row_number() over(), "should_not_add_any_rows" FROM t1;
+INSERT INTO t1 SELECT 1 + row_number() over(), "should_not_add_any_rows" FROM t1;
 
 EXECUTE populate_table;
 
-INSERT INTO t1 SELECT 10 + row_number() over(), "should repeat 4 times [11-14]" FROM t1;
+INSERT INTO t1 SELECT 10 + row_number() over(), "should repeat 2 times [11-12]" FROM t1;
 
 SELECT c1, c2 FROM t1 ORDER BY c2, c1;
 

sql/item_windowfunc.h

@@ -851,7 +851,7 @@ class Item_window_func : public Item_func_or_sum
   bool is_null()
   {
     if (force_return_blank)
-      return false;
+      return true;
 
     if (read_value_from_result_field)
       return result_field->is_null();
@@ -865,7 +865,7 @@ class Item_window_func : public Item_func_or_sum
     if (force_return_blank)
     {
       res= 0.0;
-      null_value= false;
+      null_value= true;
     }
     else if (read_value_from_result_field)
     {
@@ -886,7 +886,7 @@ class Item_window_func : public Item_func_or_sum
     if (force_return_blank)
     {
       res= 0;
-      null_value= false;
+      null_value= true;
     }
     else if (read_value_from_result_field)
     {
@@ -906,9 +906,8 @@ class Item_window_func : public Item_func_or_sum
     String *res;
     if (force_return_blank)
     {
-      null_value= false;
-      str->length(0);
-      res= str;
+      null_value= true;
+      res= NULL;
     }
     else if (read_value_from_result_field)
     {
@@ -930,9 +929,8 @@ class Item_window_func : public Item_func_or_sum
     my_decimal *res;
     if (force_return_blank)
     {
-      my_decimal_set_zero(dec);
-      null_value= false;
-      res= dec;
+      null_value= true;
+      res= NULL;
     }
     else if (read_value_from_result_field)
     {