I think that is still not really possible to do that right now.
what you can do though is putting 2 tables next to each other to get the result you are working on, like this:
Row(
children: <Widget>[
Container(
width: 100.0,
color: Colors.cyan,
child: Table(
children: [
TableRow(
children: [
Container(
color: Colors.green,
width: 50.0,
height: 50.0,
child: Text("1111111111111111111111111111111111111111111"),
),
Container(
color: Colors.red,
width: 50.0,
height: 50.0,
child: Text("2"),
),
]),
TableRow(
children: [
Container(
color: Colors.deepPurple,
width: 50.0,
height: 50.0,
child: Text("5"),
),
Container(
color: Colors.cyan,
width: 50.0,
height: 50.0,
child: Text("6"),
),
]),
TableRow(
children: [
Container(
color: Colors.amberAccent,
width: 50.0,
height: 50.0,
child: Text("7"),
),
Container(
color: Colors.black87,
width: 50.0,
height: 50.0,
child: Text("8"),
),
]),
],
),
),
Container(
width: 100.0,
color: Colors.cyan,
child: Table(
columnWidths: {
1: FractionColumnWidth(.3),
},
children: [
TableRow(
children: [
Container(
color: Colors.green,
width: 50.0,
height: 50.0,
child: Text("1111111111111111111111111111111111111111111"),
),
Container(
color: Colors.red,
width: 50.0,
height: 50.0,
child: Text("2"),
),
]),
TableRow(
children: [
Container(
color: Colors.deepPurple,
width: 50.0,
height: 100.0,
child: Text("5"),
),
Container(
color: Colors.cyan,
width: 50.0,
height: 100.0,
child: Text("6"),
),
]),
],
),
),
],
),