mysql: Fix ColumnNumber() panic with nil Resultset (#968)

* mysql: Fix ColumnNumber() panic with nil Resultset

* Add more comments

* Fix comments

---------

Co-authored-by: lance6716 <lance6716@gmail.com>

Author: dveeden

mysql/resultset.go

@@ -79,14 +79,23 @@ func (r *Resultset) Reset(fieldsCount int) {
 	}
 }
 
+// RowNumber is returning the number of rows in the [Resultset].
+//
+// For a nil [Resultset] 0 is returned.
 func (r *Resultset) RowNumber() int {
 	if r == nil {
 		return 0
 	}
 	return len(r.Values)
 }
 
+// ColumnNumber is returning the number of fields in the [Resultset].
+//
+// For a nil [Resultset] 0 is returned.
 func (r *Resultset) ColumnNumber() int {
+	if r == nil {
+		return 0
+	}
 	return len(r.Fields)
 }
 

mysql/resultset_test.go

@@ -0,0 +1,10 @@
+package mysql
+
+import "testing"
+
+func TestColumnNumber(t *testing.T) {
+	r := Result{}
+	// Make sure ColumnNumber doesn't panic if ResultSet is nil
+	// https://github.com/go-mysql-org/go-mysql/issues/964
+	r.ColumnNumber()
+}