Bug#41627 Illegal mix of collations in LEAST / GREATEST / CASE

Don't throw an error after checking the first and the second arguments.
Continue with checking the third and higher arguments and if some of
them is stronger according to coercibility rules,
then this argument's collation is set as result collation.

mysql-test/r/ctype_collate.result

@@ -611,3 +611,22 @@ check table t1 extended;
 Table	Op	Msg_type	Msg_text
 test.t1	check	status	OK
 drop table t1;
+select least(_latin1'a',_latin2'b',_latin5'c' collate latin5_turkish_ci);
+least(_latin1'a',_latin2'b',_latin5'c' collate latin5_turkish_ci)
+a
+create table t1
+select least(_latin1'a',_latin2'b',_latin5'c' collate latin5_turkish_ci) as f1;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `f1` varchar(1) character set latin5 NOT NULL default ''
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;
+select case _latin1'a' when _latin2'b' then 1 when _latin5'c' collate
+latin5_turkish_ci then 2 else 3 end;
+case _latin1'a' when _latin2'b' then 1 when _latin5'c' collate
+latin5_turkish_ci then 2 else 3 end
+3
+select concat(_latin1'a',_latin2'b',_latin5'c' collate latin5_turkish_ci);
+concat(_latin1'a',_latin2'b',_latin5'c' collate latin5_turkish_ci)
+abc

mysql-test/t/ctype_collate.test

@@ -229,3 +229,17 @@ insert into t1 set a=0x6c;
 insert into t1 set a=0x4c98;
 check table t1 extended;
 drop table t1;
+
+#
+# Bug#41627 Illegal mix of collations in LEAST / GREATEST / CASE
+#
+select least(_latin1'a',_latin2'b',_latin5'c' collate latin5_turkish_ci);
+create table t1
+select least(_latin1'a',_latin2'b',_latin5'c' collate latin5_turkish_ci) as f1;
+show create table t1;
+drop table t1;
+
+select case _latin1'a' when _latin2'b' then 1 when _latin5'c' collate
+latin5_turkish_ci then 2 else 3 end;
+
+select concat(_latin1'a',_latin2'b',_latin5'c' collate latin5_turkish_ci);

sql/item.cc

@@ -1498,7 +1498,8 @@ bool DTCollation::aggregate(DTCollation &dt, uint flags)
     else
     {
       // Cannot apply conversion
-      set(0, DERIVATION_NONE, 0);
+      set(&my_charset_bin, DERIVATION_NONE,
+          (dt.repertoire|repertoire));
       return 1;
     }
   }
@@ -1581,15 +1582,31 @@ bool agg_item_collations(DTCollation &c, const char *fname,
 {
   uint i;
   Item **arg;
+  bool unknown_cs= 0;
+
   c.set(av[0]->collation);
   for (i= 1, arg= &av[item_sep]; i < count; i++, arg++)
   {
     if (c.aggregate((*arg)->collation, flags))
     {
+      if (c.derivation == DERIVATION_NONE &&
+          c.collation == &my_charset_bin)
+      {
+        unknown_cs= 1;
+        continue;
+      }
       my_coll_agg_error(av, count, fname, item_sep);
       return TRUE;
     }
   }
+
+  if (unknown_cs &&
+      c.derivation != DERIVATION_EXPLICIT)
+  {
+    my_coll_agg_error(av, count, fname, item_sep);
+    return TRUE;
+  }
+
   if ((flags & MY_COLL_DISALLOW_NONE) &&
       c.derivation == DERIVATION_NONE)
   {