Bug #19700: subselect returning BIGINT always returned it as SIGNED

  
The unsigned flag in Item was not propagated through the single value subqueries.
This caused the result to be treated as signed.

mysql-test/r/subselect.result

@@ -3183,3 +3183,24 @@ select * from (select min(i) from t1 where j=(select * from (select min(j) from
 min(i)
 1
 drop table t1;
+CREATE TABLE t1 (i BIGINT UNSIGNED);
+INSERT INTO t1 VALUES (10000000000000000000);
+INSERT INTO t1 VALUES (1);
+CREATE TABLE t2 (i BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (10000000000000000000);
+INSERT INTO t2 VALUES (1);
+/* simple test */
+SELECT t1.i FROM t1 JOIN t2 ON t1.i = t2.i;
+i
+10000000000000000000
+1
+/* subquery test */
+SELECT t1.i FROM t1 WHERE t1.i = (SELECT MAX(i) FROM t2);
+i
+10000000000000000000
+/* subquery test with cast*/
+SELECT t1.i FROM t1 WHERE t1.i = CAST((SELECT MAX(i) FROM t2) AS UNSIGNED);
+i
+10000000000000000000
+DROP TABLE t1;
+DROP TABLE t2;

mysql-test/t/subselect.test

@@ -2109,3 +2109,25 @@ insert into t1 values (1, 2), (2, 2), (3, 2);
 select * from (select min(i) from t1 where j=(select * from (select min(j) from t1) t2)) t3;
 drop table t1;
 
+# 
+# Bug#19700: subselect returning BIGINT always returned it as SIGNED
+#
+CREATE TABLE t1 (i BIGINT UNSIGNED);
+INSERT INTO t1 VALUES (10000000000000000000); -- > MAX SIGNED BIGINT 9323372036854775807
+INSERT INTO t1 VALUES (1);
+
+CREATE TABLE t2 (i BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (10000000000000000000); -- same as first table
+INSERT INTO t2 VALUES (1);
+
+/* simple test */
+SELECT t1.i FROM t1 JOIN t2 ON t1.i = t2.i;
+
+/* subquery test */
+SELECT t1.i FROM t1 WHERE t1.i = (SELECT MAX(i) FROM t2);
+
+/* subquery test with cast*/
+SELECT t1.i FROM t1 WHERE t1.i = CAST((SELECT MAX(i) FROM t2) AS UNSIGNED);
+
+DROP TABLE t1;
+DROP TABLE t2;

sql/item.h

@@ -2243,6 +2243,7 @@ public:
     max_length= item->max_length;
     decimals= item->decimals;
     collation.set(item->collation);
+    unsigned_flag= item->unsigned_flag;
     return 0;
   };
   virtual void store(Item *)= 0;

sql/item_subselect.cc

@@ -404,6 +404,7 @@ void Item_singlerow_subselect::fix_length_and_dec()
     engine->fix_length_and_dec(row);
     value= *row;
   }
+  unsigned_flag= value->unsigned_flag;
   /*
     If there are not tables in subquery then ability to have NULL value
     depends on SELECT list (if single row subquery have tables then it