diff --git a/datatypes/mcs_datatype.h b/datatypes/mcs_datatype.h
index 2bdfada62..93b673070 100644
--- a/datatypes/mcs_datatype.h
+++ b/datatypes/mcs_datatype.h
@@ -471,10 +471,7 @@ inline bool isDecimal(const datatypes::SystemCatalog::ColDataType type)
   return (type == datatypes::SystemCatalog::DECIMAL || type == datatypes::SystemCatalog::UDECIMAL);
 }
 
-/** convenience function to determine if column type is an
- *  unsigned type
- */
-inline bool isUnsigned(const datatypes::SystemCatalog::ColDataType type)
+inline bool isUnsignedInteger(const datatypes::SystemCatalog::ColDataType type)
 {
   switch (type)
   {
@@ -482,7 +479,22 @@ inline bool isUnsigned(const datatypes::SystemCatalog::ColDataType type)
     case datatypes::SystemCatalog::USMALLINT:
     case datatypes::SystemCatalog::UMEDINT:
     case datatypes::SystemCatalog::UINT:
-    case datatypes::SystemCatalog::UBIGINT:
+    case datatypes::SystemCatalog::UBIGINT: return true;
+
+    default: return false;
+  }
+}
+
+/** convenience function to determine if column type is an
+ *  unsigned type
+ */
+inline bool isUnsigned(const datatypes::SystemCatalog::ColDataType type)
+{
+  if (isUnsignedInteger(type)) 
+    return true;
+
+  switch (type)
+  {
     case datatypes::SystemCatalog::CHAR:
     case datatypes::SystemCatalog::VARCHAR:
     case datatypes::SystemCatalog::TEXT:
@@ -506,6 +518,62 @@ inline bool isSignedInteger(const datatypes::SystemCatalog::ColDataType type)
   }
 }
 
+inline bool sameSignednessInteger(const datatypes::SystemCatalog::ColDataType type1, const datatypes::SystemCatalog::ColDataType type2)
+{
+  return (isSignedInteger(type1) && isSignedInteger(type2)) || (isUnsignedInteger(type1) && isUnsignedInteger(type2));
+}
+
+inline bool differentSignednessInteger(const datatypes::SystemCatalog::ColDataType type1, const datatypes::SystemCatalog::ColDataType type2)
+{
+  return (isSignedInteger(type1) && isUnsignedInteger(type2)) || (isUnsignedInteger(type1) && isSignedInteger(type2));
+}
+
+inline void promoteSignedInteger(datatypes::SystemCatalog::TypeHolderStd& unionedType)
+{
+  switch (unionedType.colDataType)
+  {
+    case datatypes::SystemCatalog::TINYINT:
+    case datatypes::SystemCatalog::UTINYINT:
+    {
+      unionedType.colDataType = datatypes::SystemCatalog::SMALLINT;
+      unionedType.colWidth = 2;
+      return;
+    }
+    case datatypes::SystemCatalog::SMALLINT:
+    case datatypes::SystemCatalog::USMALLINT:
+    {
+      unionedType.colDataType = datatypes::SystemCatalog::MEDINT;
+      unionedType.colWidth = 4;
+      return;
+    }
+    case datatypes::SystemCatalog::MEDINT:
+    case datatypes::SystemCatalog::UMEDINT:
+    {
+      unionedType.colDataType = datatypes::SystemCatalog::INT;
+      unionedType.colWidth = 4;
+      return;
+    }
+    case datatypes::SystemCatalog::INT:
+    case datatypes::SystemCatalog::UINT:
+    {
+      unionedType.colDataType = datatypes::SystemCatalog::BIGINT;
+      unionedType.colWidth = 8;
+      return;
+    }
+    case datatypes::SystemCatalog::BIGINT:
+    case datatypes::SystemCatalog::UBIGINT:
+    {
+      unionedType.colDataType = datatypes::SystemCatalog::DECIMAL;
+      unionedType.colWidth = MAXDECIMALWIDTH;
+      unionedType.precision = datatypes::INT128MAXPRECISION;
+      unionedType.scale = 0;
+      return;
+    } 
+
+    default: idbassert(0); throw std::logic_error("datatypes::upcastSignedInteger: bad data type");
+  }
+}
+
 /**
     @brief The method netects whether type sum and avg aggregate will have
     wide decimal underlying type
diff --git a/mysql-test/columnstore/basic/r/union.result b/mysql-test/columnstore/basic/r/union.result
index 894367865..867bccf76 100644
--- a/mysql-test/columnstore/basic/r/union.result
+++ b/mysql-test/columnstore/basic/r/union.result
@@ -6,21 +6,639 @@ USE mcs_union;
 # MCOL-4700 Wrong result of a UNION for INT and INT UNSIGNED
 #
 CREATE TABLE t1 (a INT, b INT UNSIGNED);
-INSERT INTO t1 VALUES (-1,1);
+INSERT INTO t1 VALUES (-1, 1), (-1, 1), (-2, 2);
+SELECT * FROM (SELECT * FROM t1 UNION SELECT * FROM t1) tu ORDER BY b;
+a	b
+-1	1
+-2	2
+SELECT * FROM (SELECT a FROM t1 UNION SELECT b FROM t1) tu ORDER BY a;
+a
+-2
+-1
+1
+2
+SELECT * FROM (SELECT b FROM t1 UNION SELECT a FROM t1) tu ORDER BY b;
+b
+-2
+-1
+1
+2
+DROP TABLE t1;
+#
+# Multiple Columns Union
+#
+CREATE TABLE t1 (a INT, b INT, c INT);
+INSERT INTO t1 VALUES (-1, 1, 0), (-2, 2, 0), (-3, 3, 0), (-4, 4, 0), (-5, 5, 0), (-1, 1, 0), (-2, 2, 0), (-3, 3, 0), (-4, 4, 0), (-5, 5, 0);
+SELECT * FROM (SELECT * FROM t1 UNION ALL SELECT * FROM t1) tu ORDER BY b;
+a	b	c
+-1	1	0
+-1	1	0
+-1	1	0
+-1	1	0
+-2	2	0
+-2	2	0
+-2	2	0
+-2	2	0
+-3	3	0
+-3	3	0
+-3	3	0
+-3	3	0
+-4	4	0
+-4	4	0
+-4	4	0
+-4	4	0
+-5	5	0
+-5	5	0
+-5	5	0
+-5	5	0
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT b FROM t1) tu ORDER BY a;
+a
+-5
+-5
+-4
+-4
+-3
+-3
+-2
+-2
+-1
+-1
+1
+1
+2
+2
+3
+3
+4
+4
+5
+5
+SELECT * FROM (SELECT b FROM t1 UNION ALL SELECT a FROM t1) tu ORDER BY b;
+b
+-5
+-5
+-4
+-4
+-3
+-3
+-2
+-2
+-1
+-1
+1
+1
+2
+2
+3
+3
+4
+4
+5
+5
+DROP TABLE t1;
+#
+# Same Int Type Union
+#
+CREATE TABLE t1 (a INT UNSIGNED, b INT UNSIGNED);
+INSERT INTO t1 VALUES (1, 1), (1, 1), (2, 1), (2, 1), (3, 2), (4, 2), (5, 2);
+SELECT * FROM (SELECT a FROM t1 UNION SELECT b FROM t1) tu ORDER BY a;
+a
+1
+2
+3
+4
+5
+SELECT * FROM (SELECT b FROM t1 UNION SELECT a FROM t1) tu ORDER BY b;
+b
+1
+2
+3
+4
+5
+SELECT * FROM (SELECT * FROM t1 UNION SELECT * FROM t1) tu ORDER BY a;
+a	b
+1	1
+2	1
+3	2
+4	2
+5	2
+DROP TABLE t1;
+CREATE TABLE t1 (a INT, b INT);
+INSERT INTO t1 VALUES (-1, -1), (-1, -1), (2, 1), (2, 1), (3, 2), (4, 2), (5, 2);
 SELECT * FROM (SELECT a FROM t1 UNION SELECT b FROM t1) tu ORDER BY a;
 a
 -1
 1
+2
+3
+4
+5
 SELECT * FROM (SELECT b FROM t1 UNION SELECT a FROM t1) tu ORDER BY b;
 b
 -1
 1
+2
+3
+4
+5
+SELECT * FROM (SELECT * FROM t1 UNION SELECT * FROM t1) tu ORDER BY a;
+a	b
+-1	-1
+2	1
+3	2
+4	2
+5	2
 DROP TABLE t1;
+#
+# Signed Int Union
+#
+CREATE TABLE t1 (a TINYINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFFFF80 AS SIGNED)+2),(-1),(0),(1),(0x7F);
+CREATE TABLE t2 (a SMALLINT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFFFFFF8000 AS SIGNED)+2),(-1),(0),(1),(0x7FFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-32766
+-126
+-1
+-1
+0
+0
+1
+1
+127
+32767
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-32766
+-126
+-1
+-1
+0
+0
+1
+1
+127
+32767
+DROP TABLE t2;
+CREATE TABLE t2 (a MEDIUMINT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-8388606
+-126
+-1
+-1
+0
+0
+1
+1
+127
+8388607
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-8388606
+-126
+-1
+-1
+0
+0
+1
+1
+127
+8388607
+DROP TABLE t2;
+CREATE TABLE t2 (a INT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-2147483646
+-126
+-1
+-1
+0
+0
+1
+1
+127
+2147483647
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-2147483646
+-126
+-1
+-1
+0
+0
+1
+1
+127
+2147483647
+DROP TABLE t2;
+CREATE TABLE t2 (a BIGINT);
+INSERT INTO t2 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-9223372036854775806
+-126
+-1
+-1
+0
+0
+1
+1
+127
+9223372036854775807
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-9223372036854775806
+-126
+-1
+-1
+0
+0
+1
+1
+127
+9223372036854775807
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a SMALLINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFF8000 AS SIGNED)+2),(-1),(0),(1),(0x7FFF);
+CREATE TABLE t2 (a MEDIUMINT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-8388606
+-32766
+-1
+-1
+0
+0
+1
+1
+32767
+8388607
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-8388606
+-32766
+-1
+-1
+0
+0
+1
+1
+32767
+8388607
+DROP TABLE t2;
+CREATE TABLE t2 (a INT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-2147483646
+-32766
+-1
+-1
+0
+0
+1
+1
+32767
+2147483647
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-2147483646
+-32766
+-1
+-1
+0
+0
+1
+1
+32767
+2147483647
+DROP TABLE t2;
+CREATE TABLE t2 (a BIGINT);
+INSERT INTO t2 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-9223372036854775806
+-32766
+-1
+-1
+0
+0
+1
+1
+32767
+9223372036854775807
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-9223372036854775806
+-32766
+-1
+-1
+0
+0
+1
+1
+32767
+9223372036854775807
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a MEDIUMINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
+CREATE TABLE t2 (a INT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-2147483646
+-8388606
+-1
+-1
+0
+0
+1
+1
+8388607
+2147483647
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-2147483646
+-8388606
+-1
+-1
+0
+0
+1
+1
+8388607
+2147483647
+DROP TABLE t2;
+CREATE TABLE t2 (a BIGINT);
+INSERT INTO t2 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-9223372036854775806
+-8388606
+-1
+-1
+0
+0
+1
+1
+8388607
+9223372036854775807
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-9223372036854775806
+-8388606
+-1
+-1
+0
+0
+1
+1
+8388607
+9223372036854775807
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
+CREATE TABLE t2 (a BIGINT);
+INSERT INTO t2 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-9223372036854775806
+-2147483646
+-1
+-1
+0
+0
+1
+1
+2147483647
+9223372036854775807
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-9223372036854775806
+-2147483646
+-1
+-1
+0
+0
+1
+1
+2147483647
+9223372036854775807
+DROP TABLE t1,t2;
+#
+# Unsigned Int Union
+#
+CREATE TABLE t1 (a TINYINT UNSIGNED);
+INSERT INTO t1 VALUES (0),(1),(0xFF-2);
+CREATE TABLE t2 (a SMALLINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+253
+65533
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+253
+65533
+DROP TABLE t2;
+CREATE TABLE t2 (a MEDIUMINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+253
+16777213
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+253
+16777213
+DROP TABLE t2;
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+253
+4294967293
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+253
+4294967293
+DROP TABLE t2;
+CREATE TABLE t2 (a BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+253
+18446744073709551613
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+253
+18446744073709551613
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a SMALLINT UNSIGNED);
+INSERT INTO t1 VALUES (0),(1),(0xFFFF-2);
+CREATE TABLE t2 (a MEDIUMINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+65533
+16777213
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+65533
+16777213
+DROP TABLE t2;
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+65533
+4294967293
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+65533
+4294967293
+DROP TABLE t2;
+CREATE TABLE t2 (a BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+65533
+18446744073709551613
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+65533
+18446744073709551613
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a MEDIUMINT UNSIGNED);
+INSERT INTO t1 VALUES (0),(1),(0xFFFFFF-2);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+16777213
+4294967293
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+16777213
+4294967293
+DROP TABLE t2;
+CREATE TABLE t2 (a BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+16777213
+18446744073709551613
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+16777213
+18446744073709551613
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a INT UNSIGNED);
+INSERT INTO t1 VALUES (0),(1),(0xFFFFFFFF-2);
+CREATE TABLE t2 (a BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+0
+0
+1
+1
+4294967293
+18446744073709551613
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+0
+0
+1
+1
+4294967293
+18446744073709551613
+DROP TABLE t1,t2;
+#
+# Same Size Different Signedness Int Union
+#
 CREATE TABLE t1 (a TINYINT);
 INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFFFF80 AS SIGNED)+2),(-1),(0),(1),(0x7F);
 CREATE TABLE t2 (a TINYINT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFF-2);
-(SELECT a FROM t1 UNION ALL SELECT a FROM t2) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
 a
 -126
 -1
@@ -30,7 +648,7 @@ a
 1
 127
 253
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 a
 -126
 -1
@@ -43,9 +661,9 @@ a
 DROP TABLE t1,t2;
 CREATE TABLE t1 (a SMALLINT);
 INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFF8000 AS SIGNED)+2),(-1),(0),(1),(0x7FFF);
-CREATE TABLE t2 (a INT UNSIGNED);
+CREATE TABLE t2 (a SMALLINT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFFFF-2);
-(SELECT a FROM t1 UNION ALL SELECT * FROM t2) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT * FROM t2) tu ORDER BY a;
 a
 -32766
 -1
@@ -55,7 +673,7 @@ a
 1
 32767
 65533
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 a
 -32766
 -1
@@ -68,9 +686,9 @@ a
 DROP TABLE t1,t2;
 CREATE TABLE t1 (a MEDIUMINT);
 INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
-CREATE TABLE t2 (a INT UNSIGNED);
+CREATE TABLE t2 (a MEDIUMINT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
-(SELECT a FROM t1 UNION ALL SELECT a FROM t2) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
 a
 -8388606
 -1
@@ -80,7 +698,7 @@ a
 1
 8388607
 16777213
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 a
 -8388606
 -1
@@ -95,7 +713,7 @@ CREATE TABLE t1 (a INT);
 INSERT INTO t1 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
 CREATE TABLE t2 (a INT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFF-2);
-(SELECT a FROM t1 UNION ALL SELECT a FROM t2) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
 a
 -2147483646
 -1
@@ -105,7 +723,7 @@ a
 1
 2147483647
 4294967293
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 a
 -2147483646
 -1
@@ -120,7 +738,7 @@ CREATE TABLE t1 (a BIGINT);
 INSERT INTO t1 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
 CREATE TABLE t2 (a BIGINT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
-(SELECT a FROM t1 UNION ALL SELECT a FROM t2) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
 a
 -9223372036854775806
 -1
@@ -130,7 +748,7 @@ a
 1
 9223372036854775807
 18446744073709551613
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 a
 -9223372036854775806
 -1
@@ -141,4 +759,107 @@ a
 9223372036854775807
 18446744073709551613
 DROP TABLE t1,t2;
+#
+# Different Size Different Signedness Int Union
+#
+CREATE TABLE t1 (a TINYINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFFFF80 AS SIGNED)+2),(-1),(0),(1),(0x7F);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT * FROM t2) tu ORDER BY a;
+a
+-126
+-1
+0
+0
+1
+1
+127
+65533
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-126
+-1
+0
+0
+1
+1
+127
+65533
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a SMALLINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFF8000 AS SIGNED)+2),(-1),(0),(1),(0x7FFF);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT * FROM t2) tu ORDER BY a;
+a
+-32766
+-1
+0
+0
+1
+1
+32767
+65533
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-32766
+-1
+0
+0
+1
+1
+32767
+65533
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a MEDIUMINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-8388606
+-1
+0
+0
+1
+1
+8388607
+16777213
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-8388606
+-1
+0
+0
+1
+1
+8388607
+16777213
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a BIGINT);
+INSERT INTO t1 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+a
+-9223372036854775806
+-1
+0
+0
+1
+1
+16777213
+9223372036854775807
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+a
+-9223372036854775806
+-1
+0
+0
+1
+1
+16777213
+9223372036854775807
+DROP TABLE t1,t2;
 DROP DATABASE mcs_union;
diff --git a/mysql-test/columnstore/basic/t/union.test b/mysql-test/columnstore/basic/t/union.test
index abae3c497..eed88576a 100644
--- a/mysql-test/columnstore/basic/t/union.test
+++ b/mysql-test/columnstore/basic/t/union.test
@@ -14,49 +14,263 @@ USE mcs_union;
 --echo #
 
 CREATE TABLE t1 (a INT, b INT UNSIGNED);
-INSERT INTO t1 VALUES (-1,1);
+INSERT INTO t1 VALUES (-1, 1), (-1, 1), (-2, 2);
+SELECT * FROM (SELECT * FROM t1 UNION SELECT * FROM t1) tu ORDER BY b;
 SELECT * FROM (SELECT a FROM t1 UNION SELECT b FROM t1) tu ORDER BY a;
 SELECT * FROM (SELECT b FROM t1 UNION SELECT a FROM t1) tu ORDER BY b;
 DROP TABLE t1;
 
+--echo #
+--echo # Multiple Columns Union
+--echo #
+
+CREATE TABLE t1 (a INT, b INT, c INT);
+INSERT INTO t1 VALUES (-1, 1, 0), (-2, 2, 0), (-3, 3, 0), (-4, 4, 0), (-5, 5, 0), (-1, 1, 0), (-2, 2, 0), (-3, 3, 0), (-4, 4, 0), (-5, 5, 0);
+SELECT * FROM (SELECT * FROM t1 UNION ALL SELECT * FROM t1) tu ORDER BY b;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT b FROM t1) tu ORDER BY a;
+SELECT * FROM (SELECT b FROM t1 UNION ALL SELECT a FROM t1) tu ORDER BY b;
+DROP TABLE t1;
+
+--echo #
+--echo # Same Int Type Union
+--echo #
+
+CREATE TABLE t1 (a INT UNSIGNED, b INT UNSIGNED);
+INSERT INTO t1 VALUES (1, 1), (1, 1), (2, 1), (2, 1), (3, 2), (4, 2), (5, 2);
+SELECT * FROM (SELECT a FROM t1 UNION SELECT b FROM t1) tu ORDER BY a;
+SELECT * FROM (SELECT b FROM t1 UNION SELECT a FROM t1) tu ORDER BY b;
+SELECT * FROM (SELECT * FROM t1 UNION SELECT * FROM t1) tu ORDER BY a;
+DROP TABLE t1;
+
+CREATE TABLE t1 (a INT, b INT);
+INSERT INTO t1 VALUES (-1, -1), (-1, -1), (2, 1), (2, 1), (3, 2), (4, 2), (5, 2);
+SELECT * FROM (SELECT a FROM t1 UNION SELECT b FROM t1) tu ORDER BY a;
+SELECT * FROM (SELECT b FROM t1 UNION SELECT a FROM t1) tu ORDER BY b;
+SELECT * FROM (SELECT * FROM t1 UNION SELECT * FROM t1) tu ORDER BY a;
+DROP TABLE t1;
+
+--echo #
+--echo # Signed Int Union
+--echo #
+
+CREATE TABLE t1 (a TINYINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFFFF80 AS SIGNED)+2),(-1),(0),(1),(0x7F);
+CREATE TABLE t2 (a SMALLINT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFFFFFF8000 AS SIGNED)+2),(-1),(0),(1),(0x7FFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a MEDIUMINT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a INT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a BIGINT);
+INSERT INTO t2 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a SMALLINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFF8000 AS SIGNED)+2),(-1),(0),(1),(0x7FFF);
+CREATE TABLE t2 (a MEDIUMINT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a INT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a BIGINT);
+INSERT INTO t2 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a MEDIUMINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
+CREATE TABLE t2 (a INT);
+INSERT INTO t2 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a BIGINT);
+INSERT INTO t2 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
+CREATE TABLE t2 (a BIGINT);
+INSERT INTO t2 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+--echo #
+--echo # Unsigned Int Union
+--echo #
+
+CREATE TABLE t1 (a TINYINT UNSIGNED);
+INSERT INTO t1 VALUES (0),(1),(0xFF-2);
+CREATE TABLE t2 (a SMALLINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a MEDIUMINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a SMALLINT UNSIGNED);
+INSERT INTO t1 VALUES (0),(1),(0xFFFF-2);
+CREATE TABLE t2 (a MEDIUMINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a MEDIUMINT UNSIGNED);
+INSERT INTO t1 VALUES (0),(1),(0xFFFFFF-2);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t2;
+
+CREATE TABLE t2 (a BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a INT UNSIGNED);
+INSERT INTO t1 VALUES (0),(1),(0xFFFFFFFF-2);
+CREATE TABLE t2 (a BIGINT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+--echo #
+--echo # Same Size Different Signedness Int Union
+--echo #
+
 CREATE TABLE t1 (a TINYINT);
 INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFFFF80 AS SIGNED)+2),(-1),(0),(1),(0x7F);
 CREATE TABLE t2 (a TINYINT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFF-2);
-(SELECT a FROM t1 UNION ALL SELECT a FROM t2) ORDER BY a;
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 DROP TABLE t1,t2;
 
 CREATE TABLE t1 (a SMALLINT);
 INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFF8000 AS SIGNED)+2),(-1),(0),(1),(0x7FFF);
-CREATE TABLE t2 (a INT UNSIGNED);
+CREATE TABLE t2 (a SMALLINT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFFFF-2);
-(SELECT a FROM t1 UNION ALL SELECT * FROM t2) ORDER BY a;
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT * FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 DROP TABLE t1,t2;
 
 CREATE TABLE t1 (a MEDIUMINT);
 INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
-CREATE TABLE t2 (a INT UNSIGNED);
+CREATE TABLE t2 (a MEDIUMINT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
-(SELECT a FROM t1 UNION ALL SELECT a FROM t2) ORDER BY a;
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 DROP TABLE t1,t2;
 
 CREATE TABLE t1 (a INT);
 INSERT INTO t1 VALUES (CAST(0xFFFFFFFF80000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFF);
 CREATE TABLE t2 (a INT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFF-2);
-(SELECT a FROM t1 UNION ALL SELECT a FROM t2) ORDER BY a;
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 DROP TABLE t1,t2;
 
 CREATE TABLE t1 (a BIGINT);
 INSERT INTO t1 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
 CREATE TABLE t2 (a BIGINT UNSIGNED);
 INSERT INTO t2 VALUES (0),(1),(0xFFFFFFFFFFFFFFFF-2);
-(SELECT a FROM t1 UNION ALL SELECT a FROM t2) ORDER BY a;
-(SELECT a FROM t2 UNION ALL SELECT a FROM t1) ORDER BY a;
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+--echo #
+--echo # Different Size Different Signedness Int Union
+--echo #
+
+CREATE TABLE t1 (a TINYINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFFFF80 AS SIGNED)+2),(-1),(0),(1),(0x7F);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT * FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a SMALLINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFFFF8000 AS SIGNED)+2),(-1),(0),(1),(0x7FFF);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT * FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a MEDIUMINT);
+INSERT INTO t1 VALUES (CAST(0xFFFFFFFFFF800000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFF);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a BIGINT);
+INSERT INTO t1 VALUES (CAST(0x8000000000000000 AS SIGNED)+2),(-1),(0),(1),(0x7FFFFFFFFFFFFFFF);
+CREATE TABLE t2 (a INT UNSIGNED);
+INSERT INTO t2 VALUES (0),(1),(0xFFFFFF-2);
+SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
+SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 DROP TABLE t1,t2;
 
 DROP DATABASE mcs_union;
diff --git a/utils/dataconvert/dataconvert.cpp b/utils/dataconvert/dataconvert.cpp
index 37ff38c4e..5f3af5a2e 100644
--- a/utils/dataconvert/dataconvert.cpp
+++ b/utils/dataconvert/dataconvert.cpp
@@ -2984,25 +2984,29 @@ void DataConvert::joinColTypeForUnion(datatypes::SystemCatalog::TypeHolderStd& u
             break;
           }
 
-          if (type.colWidth > unionedType.colWidth)
+          if (type.colDataType == unionedType.colDataType)
           {
-            unionedType.colDataType = type.colDataType;
-            unionedType.colWidth = type.colWidth;
+            if (type.colWidth > unionedType.colWidth)
+              unionedType.colWidth = type.colWidth;
+          }
+          else if (sameSignednessInteger(unionedType.colDataType, type.colDataType))
+          {
+            // Keep the signedness on the larger data type.
+            if (type.colWidth > unionedType.colWidth)
+            {
+              unionedType.colDataType = type.colDataType;
+              unionedType.colWidth = type.colWidth;
+            }
+          }
+          else if (differentSignednessInteger(unionedType.colDataType, type.colDataType))
+          {
+            // unionedType must be signed integer with upcasted size to prevent overflow & underflow.
+            if (type.colWidth > unionedType.colWidth)
+              unionedType.colDataType = type.colDataType;
+            promoteSignedInteger(unionedType);
           }
 
-          // If same size but different signedness
-          if (type.colWidth == unionedType.colWidth &&
-              ((!isUnsigned(unionedType.colDataType) && isUnsigned(type.colDataType)) ||
-               (!isUnsigned(type.colDataType) && isUnsigned(unionedType.colDataType))))
-          {
-            unionedType.colDataType = datatypes::SystemCatalog::DECIMAL;
-            unionedType.colWidth = datatypes::Decimal::isWideDecimalTypeByPrecision(unionedType.precision)
-                                       ? datatypes::MAXDECIMALWIDTH
-                                       : datatypes::MAXLEGACYWIDTH;
-          }
-
-          if (type.colDataType == datatypes::SystemCatalog::DECIMAL ||
-              type.colDataType == datatypes::SystemCatalog::UDECIMAL)
+          if (isDecimal(type.colDataType))
           {
             unionedType.colDataType = datatypes::SystemCatalog::DECIMAL;
           }