MDEV-8630 Datetime value dropped in "INSERT ... SELECT ... ON DUPLICATE KEY"

Item_func_coalesce::fix_length_and_dec() calls
Item_func::count_string_result_length()) which called agg_arg_charsets()
with wrong flags, so the collation derivation of the COALESCE result was
not properly set to DERIVATION_COERCIBLE. It erroneously stayed
DERIVATION_NUMERIC. So GREATEST() misinterpreted the argument as
a number rather that a string and did not calculate its own length properly.

mysql-test/r/ctype_utf8.result

@@ -5777,5 +5777,32 @@ SELECT (SELECT CONCAT(a),1 FROM t1) <=> (SELECT CONCAT(a),1 FROM t2);
 ERROR 21000: Subquery returns more than 1 row
 DROP TABLE t1, t2;
 #
+# MDEV-8630 Datetime value dropped in "INSERT ... SELECT ... ON DUPLICATE KEY"
+#
+SET NAMES utf8;
+CREATE TABLE t1 (id2 int, ts timestamp);
+INSERT INTO t1 VALUES (1,'2012-06-11 15:17:34'),(2,'2012-06-11 15:18:24');
+CREATE TABLE t2 AS SELECT
+COALESCE(ts, 0) AS c0,
+GREATEST(COALESCE(ts, 0), COALESCE(ts, 0)) AS c1,
+GREATEST(CASE WHEN 1 THEN ts ELSE 0 END, CASE WHEN 1 THEN ts ELSE 0 END) AS c2,
+GREATEST(IFNULL(ts,0), IFNULL(ts,0)) AS c3,
+GREATEST(IF(1,ts,0), IF(1,ts,0)) AS c4
+FROM t1;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `c0` varchar(19) CHARACTER SET utf8 NOT NULL DEFAULT '',
+  `c1` varchar(19) CHARACTER SET utf8 NOT NULL DEFAULT '',
+  `c2` varchar(19) CHARACTER SET utf8 NOT NULL DEFAULT '',
+  `c3` varchar(19) CHARACTER SET utf8 NOT NULL DEFAULT '',
+  `c4` varchar(19) CHARACTER SET utf8 NOT NULL DEFAULT ''
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+SELECT * FROM t2;
+c0	c1	c2	c3	c4
+2012-06-11 15:17:34	2012-06-11 15:17:34	2012-06-11 15:17:34	2012-06-11 15:17:34	2012-06-11 15:17:34
+2012-06-11 15:18:24	2012-06-11 15:18:24	2012-06-11 15:18:24	2012-06-11 15:18:24	2012-06-11 15:18:24
+DROP TABLE t2, t1;
+#
 # End of 5.5 tests
 #

mysql-test/t/ctype_utf8.test

@@ -1631,6 +1631,22 @@ INSERT INTO t2 VALUES ('aaa');
 SELECT (SELECT CONCAT(a),1 FROM t1) <=> (SELECT CONCAT(a),1 FROM t2);
 DROP TABLE t1, t2;
 
+--echo #
+--echo # MDEV-8630 Datetime value dropped in "INSERT ... SELECT ... ON DUPLICATE KEY"
+--echo #
+SET NAMES utf8;
+CREATE TABLE t1 (id2 int, ts timestamp);
+INSERT INTO t1 VALUES (1,'2012-06-11 15:17:34'),(2,'2012-06-11 15:18:24');
+CREATE TABLE t2 AS SELECT
+  COALESCE(ts, 0) AS c0,
+  GREATEST(COALESCE(ts, 0), COALESCE(ts, 0)) AS c1,
+  GREATEST(CASE WHEN 1 THEN ts ELSE 0 END, CASE WHEN 1 THEN ts ELSE 0 END) AS c2,
+  GREATEST(IFNULL(ts,0), IFNULL(ts,0)) AS c3,
+  GREATEST(IF(1,ts,0), IF(1,ts,0)) AS c4
+FROM t1;
+SHOW CREATE TABLE t2;
+SELECT * FROM t2;
+DROP TABLE t2, t1;
 
 --echo #
 --echo # End of 5.5 tests

sql/item_func.cc

@@ -719,7 +719,7 @@ void Item_func::count_real_length()
 bool Item_func::count_string_result_length(enum_field_types field_type,
                                            Item **items, uint nitems)
 {
-  if (agg_arg_charsets(collation, items, nitems, MY_COLL_ALLOW_CONV, 1))
+  if (agg_arg_charsets_for_string_result(collation, items, nitems, 1))
     return true;
   if (is_temporal_type(field_type))
     count_datetime_length(items, nitems);