Rows.Scan can ignore column with nil

fixes #130

query.go

@@ -233,8 +233,8 @@ func (e scanArgError) Error() string {
 
 // Scan reads the values from the current row into dest values positionally.
 // dest can include pointers to core types, values implementing the Scanner
-// interface, and []byte. []byte will skip the decoding process and directly
+// interface, []byte, and nil. []byte will skip the decoding process and directly
-// copy the raw bytes received from PostgreSQL.
+// copy the raw bytes received from PostgreSQL. nil will skip the value entirely.
 func (rows *Rows) Scan(dest ...interface{}) (err error) {
 	if len(rows.fields) != len(dest) {
 		err = fmt.Errorf("Scan received wrong number of arguments, got %d but expected %d", len(dest), len(rows.fields))
@@ -245,6 +245,10 @@ func (rows *Rows) Scan(dest ...interface{}) (err error) {
 	for i, d := range dest {
 		vr, _ := rows.nextColumn()
 
+		if d == nil {
+			continue
+		}
+
 		// Check for []byte first as we allow sidestepping the decoding process and retrieving the raw bytes
 		if b, ok := d.(*[]byte); ok {
 			// If it actually is a bytea then pass it through decodeBytea (so it can be decoded if it is in text format)

query_test.go

@@ -218,6 +218,40 @@ func TestConnQueryReadTooManyValues(t *testing.T) {
 	ensureConnValid(t, conn)
 }
 
+func TestConnQueryScanIgnoreColumn(t *testing.T) {
+	t.Parallel()
+
+	conn := mustConnect(t, *defaultConnConfig)
+	defer closeConn(t, conn)
+
+	rows, err := conn.Query("select 1::int8, 2::int8, 3::int8")
+	if err != nil {
+		t.Fatalf("conn.Query failed: %v", err)
+	}
+
+	ok := rows.Next()
+	if !ok {
+		t.Fatal("rows.Next terminated early")
+	}
+
+	var n, m int64
+	err = rows.Scan(&n, nil, &m)
+	if err != nil {
+		t.Fatalf("rows.Scan failed: %v", err)
+	}
+	rows.Close()
+
+	if n != 1 {
+		t.Errorf("Expected n to equal 1, but it was %d", n)
+	}
+
+	if m != 3 {
+		t.Errorf("Expected n to equal 3, but it was %d", m)
+	}
+
+	ensureConnValid(t, conn)
+}
+
 func TestConnQueryScanner(t *testing.T) {
 	t.Parallel()