Fix bug #12537 UNION produces longtext instead of varchar

Item::tmp_table_field_from_field_type() and create_tmp_field_from_item()
was converting string field to blob depending on byte-wise length instead of
character length, which results in converting valid varchar string with
length == 86 to longtext.

Made that functions above take into account max width of character when
converting string fields to blobs.


sql/item.cc:
  Fix bug #12537 UNION produces longtext instead of varchar
  Item::tmp_table_field_from_field_type() now taking into account max char width when creating tmp field for string fields.
sql/sql_select.cc:
  Fix bug #12537 UNION produces longtext instead of varchar
   create_tmp_field_from_item()now taking into account max char width when creating tmp field for string fields.
mysql-test/r/create.result:
  Test case for bug #12537 UNION produces longtext instead of varchar
mysql-test/t/create.test:
  Test case for bug #12537 UNION produces longtext instead of varchar

1 files changed, 7 insertions, 0 deletions

diff --git a/mysql-test/r/create.result b/mysql-test/r/create.result
index 00bc0320028..95757fbd7dc 100644
--- a/mysql-test/r/create.result
+++ b/mysql-test/r/create.result
@@ -580,6 +580,13 @@ ERROR 42000: Incorrect database name 'xyz'
 create table t1(t1.name int);
 create table t2(test.t2.name int);
 drop table t1,t2;
+CREATE TABLE t1 (f1 VARCHAR(255) CHARACTER SET utf8);
+CREATE TABLE t2 AS SELECT LEFT(f1,86) AS f2 FROM t1 UNION SELECT LEFT(f1,86)
+AS f2 FROM t1;
+DESC t2;
+Field	Type	Null	Key	Default	Extra
+f2	varchar(86)	YES		NULL	
+DROP TABLE t1,t2;
 create database mysqltest;
 use mysqltest;
 drop database mysqltest;