Backport of the fix for bug #33969: Updating a text field via a

left join 

When creating a temporary TEXT/BLOB field from an Item in
Item::make_string_field(), the field's type was unconditionally
set to the one corresponding to the maximum length (i.e.
LONGTEXT/ LONGBLOB). This resulted in problems when exactly the
same TEXT/BLOB is type required in cases like CREATE ... SELECT
or creating internal temporary tables for joins. 

Fixed by calling a different constructor for Field_blob so that
an appropriate type is used depending on the Item's max_length
value.

mysql-test/r/type_blob.result

@@ -974,3 +974,21 @@ ERROR 42000: Display width out of range for column 'cast as char' (max = 4294967
 explain select convert(1, binary(999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999));
 ERROR 42000: Display width out of range for column 'cast as char' (max = 4294967295)
 End of 5.0 tests
+CREATE TABLE t1(id INT NOT NULL);
+CREATE TABLE t2(id INT NOT NULL, c TEXT NOT NULL);
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1, '');
+UPDATE t2 SET c = REPEAT('1', 70000);
+Warnings:
+Warning	1265	Data truncated for column 'c' at row 1
+SELECT LENGTH(c) FROM t2;
+LENGTH(c)
+65535
+UPDATE t1 LEFT JOIN t2 USING(id) SET t2.c = REPEAT('1', 70000) WHERE t1.id = 1;
+Warnings:
+Warning	1265	Data truncated for column 'c' at row 1
+SELECT LENGTH(c) FROM t2;
+LENGTH(c)
+65535
+DROP TABLE t1, t2;
+End of 5.1 tests

mysql-test/r/type_ranges.result

@@ -276,8 +276,8 @@ t1	int(1)	NULL	NO		0		#
 t2	varchar(1)	latin1_swedish_ci	NO				#	
 t3	varchar(256)	latin1_swedish_ci	NO				#	
 t4	varbinary(256)	NULL	NO				#	
-t5	longtext	latin1_swedish_ci	NO		NULL		#	
-t6	longblob	NULL	NO		NULL		#	
+t5	text	latin1_swedish_ci	NO		NULL		#	
+t6	blob	NULL	NO		NULL		#	
 t7	char(0)	latin1_swedish_ci	NO				#	
 t8	binary(0)	NULL	NO				#	
 select t1,t2,length(t3),length(t4),length(t5),length(t6),t7,t8 from t2;

mysql-test/t/type_blob.test

@@ -612,3 +612,23 @@ explain select convert(1, binary(4294967296));
 explain select convert(1, binary(999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999));
 
 --echo End of 5.0 tests
+
+#
+# Bug #33969: Updating a text field via a left join
+#
+
+CREATE TABLE t1(id INT NOT NULL);
+CREATE TABLE t2(id INT NOT NULL, c TEXT NOT NULL);
+
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1, '');
+
+UPDATE t2 SET c = REPEAT('1', 70000);
+SELECT LENGTH(c) FROM t2;
+
+UPDATE t1 LEFT JOIN t2 USING(id) SET t2.c = REPEAT('1', 70000) WHERE t1.id = 1;
+SELECT LENGTH(c) FROM t2;
+
+DROP TABLE t1, t2;
+
+--echo End of 5.1 tests

sql/item.cc

@@ -5025,7 +5025,7 @@ Field *Item::make_string_field(TABLE *table)
   DBUG_ASSERT(collation.collation);
   if (max_length/collation.collation->mbmaxlen > CONVERT_IF_BIGGER_TO_BLOB)
     field= new Field_blob(max_length, maybe_null, name,
-                          collation.collation);
+                          collation.collation, TRUE);
   /* Item_type_holder holds the exact type, do not change it */
   else if (max_length > 0 &&
       (type() != Item::TYPE_HOLDER || field_type() != MYSQL_TYPE_STRING))