IEnumerable <BitVector> enumerateCmp(JoinGraph graph, BitVector S1)
{
int ntables = graph.vertices_.Count;
Debug.Assert(S1 != SetOp.EmptySet);
// min(S1) := min({i|v_i \in S1})
int minS1 = SetOp.MinTableIndex(S1);
// B_i(W) := {vj |v_j \in W, j <= i}
// X = union (B_min(S1), S)
BitVector BminS1 = SetOp.OrderBeforeSet(minS1);
BitVector X = SetOp.Union(BminS1, S1);
// N = neighbour(S1) \ X
BitVector N = SetOp.Substract(graph.NeighboursExcluding(S1), X);
// for all(vi 2 N by descending i)
foreach (int vi in SetOp.TablesDescending(N))
{
// emit {v_i}
BitVector VI = SetOp.SingletonSet(vi);
yield return(VI);
// recursively invoke enumerateCmp(graph, {v_i}, X union (B_i intersect N))
BitVector Bi = SetOp.OrderBeforeSet(vi);
BitVector BiN = SetOp.Intersect(Bi, N);
foreach (var csg in enumerateCsgRecursive(graph,
VI, SetOp.Union(X, BiN)))
{
yield return(csg);
}
}
}
// read through join exprs and mark the contain join bits
// say T2.a = T5.a
// T2 is at tables_[3] and T5 is at tables_[7]
// then
// joinbits_[3].bits_.Set(7)
// joinbits_[7].bits_.Set(3)
//
void markJoinBitsFromJoinPred(List <Expr> preds)
{
var npreds = preds.Count;
predContained_ = new List <BitVector>(npreds);
for (int i = 0; i < npreds; i++)
{
var p = preds[i];
var i12 = ParseJoinPredExpr(p);
int i1 = i12[0], i2 = i12[1];
// there could be multiple join predicates between two relations
// so no need to verify duplicates here (!joinbits_[i1][i2])
joinbits_[i1][i2] = true;
joinbits_[i2][i1] = true;
// mark predicate containage as well
predContained_.Add(SetOp.SingletonSet(i1) | SetOp.SingletonSet(i2));
}
}
IEnumerable <BitVector> enumerateCsg(JoinGraph graph)
{
int ntables = graph.vertices_.Count;
for (int i = ntables - 1; i >= 0; i--)
{
// emit S
// S: {vi}
BitVector VI = SetOp.SingletonSet(i);
// Console.WriteLine("S: {0}", i);
yield return(VI);
// EnumerateCsgRec (G, S, X)
// X: {vj|j<=i}
BitVector X = SetOp.OrderBeforeSet(i);
foreach (var csg in enumerateCsgRecursive(graph, VI, X))
{
yield return(csg);
}
}
}