database/sql: add configuration option to ignore null values in Scan

src/database/sql/convert.go

@@ -212,6 +212,9 @@ func convertAssign(dest, src any) error {
 	return convertAssignRows(dest, src, nil)
 }
 
+// ignoreNullValues determines whether to ignore null values in SQL
+var ignoreNullValues = false
+
 // convertAssignRows copies to dest the value in src, converting it if possible.
 // An error is returned if the copy would result in loss of information.
 // dest should be a pointer type. If rows is passed in, the rows will
@@ -314,6 +317,10 @@ func convertAssignRows(dest, src any, rows *Rows) error {
 			}
 			*d = nil
 			return nil
+		default:
+			if ignoreNullValues {
+				return nil
+			}
 		}
 	// The driver is returning a cursor the client may iterate over.
 	case driver.Rows:

src/database/sql/sql_test.go

@@ -1496,6 +1496,7 @@ func TestCursorFake(t *testing.T) {
 }
 
 func TestInvalidNilValues(t *testing.T) {
+
 	var date1 time.Time
 	var date2 int
 
@@ -1546,6 +1547,91 @@ func TestInvalidNilValues(t *testing.T) {
 	}
 }
 
+func TestValidNilValues(t *testing.T) {
+	ignoreNullValues = true
+	defer func() { ignoreNullValues = false }()
+
+	var date1 time.Time
+	var int1 int
+	var float1 float64
+	var uint1 uint
+	var string1 string
+	var bool1 bool
+	type testStruct struct {
+		name string
+	}
+	var struct1 testStruct
+	var int2 int
+	int2 = 17
+
+	tests := []struct {
+		name  string
+		input any
+	}{
+		{
+			name:  "date",
+			input: &date1,
+		},
+		{
+			name:  "int",
+			input: &int1,
+		},
+		{
+			name:  "initialized int",
+			input: &int2,
+		},
+		{
+			name:  "float",
+			input: &float1,
+		},
+		{
+			name:  "uint",
+			input: &uint1,
+		},
+		{
+			name:  "string",
+			input: &string1,
+		},
+		{
+			name:  "bool",
+			input: &bool1,
+		},
+		{
+			name:  "struct",
+			input: &struct1,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			db := newTestDB(t, "people")
+			defer closeDB(t, db)
+
+			ctx, cancel := context.WithCancel(context.Background())
+			defer cancel()
+			conn, err := db.Conn(ctx)
+			if err != nil {
+				t.Fatal(err)
+			}
+			conn.dc.ci.(*fakeConn).skipDirtySession = true
+			defer conn.Close()
+
+			originalValue := tt.input
+			err = conn.QueryRowContext(ctx, "SELECT|people|bdate|age=?", 1).Scan(tt.input)
+			if err != nil {
+				t.Fatalf("expected no error when querying nil column, but get %s", err.Error())
+			} else if tt.input != originalValue {
+				t.Fatalf("expected null scan to preserve original value %v, but got %v", originalValue, tt.input)
+			}
+
+			err = conn.PingContext(ctx)
+			if err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+}
+
 func TestConnTx(t *testing.T) {
 	db := newTestDB(t, "people")
 	defer closeDB(t, db)