Exemple #1
0
 @Override
 public Expr optimize(final QueryContext qc, final VarScope scp) throws QueryException {
   // number of predicates may change in loop
   for (int p = 0; p < preds.length; p++) {
     final Expr pred = preds[p];
     if (pred instanceof CmpG || pred instanceof CmpV) {
       final Cmp cmp = (Cmp) pred;
       if (cmp.exprs[0].isFunction(Function.POSITION)) {
         final Expr e2 = cmp.exprs[1];
         final SeqType st2 = e2.seqType();
         // position() = last() -> last()
         // position() = $n (numeric) -> $n
         if (e2.isFunction(Function.LAST) || st2.one() && st2.type.isNumber()) {
           if (cmp instanceof CmpG && ((CmpG) cmp).op == OpG.EQ
               || cmp instanceof CmpV && ((CmpV) cmp).op == OpV.EQ) {
             qc.compInfo(OPTWRITE, pred);
             preds[p] = e2;
           }
         }
       }
     } else if (pred instanceof And) {
       if (!pred.has(Flag.FCS)) {
         // replace AND expression with predicates (don't swap position tests)
         qc.compInfo(OPTPRED, pred);
         final Expr[] and = ((Arr) pred).exprs;
         final int m = and.length - 1;
         final ExprList el = new ExprList(preds.length + m);
         for (final Expr e : Arrays.asList(preds).subList(0, p)) el.add(e);
         for (final Expr a : and) {
           // wrap test with boolean() if the result is numeric
           el.add(Function.BOOLEAN.get(null, info, a).optimizeEbv(qc, scp));
         }
         for (final Expr e : Arrays.asList(preds).subList(p + 1, preds.length)) el.add(e);
         preds = el.finish();
       }
     } else if (pred instanceof ANum) {
       final ANum it = (ANum) pred;
       final long i = it.itr();
       if (i == it.dbl()) {
         preds[p] = Pos.get(i, info);
       } else {
         qc.compInfo(OPTREMOVE, this, pred);
         return Empty.SEQ;
       }
     } else if (pred.isValue()) {
       if (pred.ebv(qc, info).bool(info)) {
         qc.compInfo(OPTREMOVE, this, pred);
         preds = Array.delete(preds, p--);
       } else {
         // handle statically known predicates
         qc.compInfo(OPTREMOVE, this, pred);
         return Empty.SEQ;
       }
     }
   }
   return this;
 }
Exemple #2
0
  @Override
  public Expr optimize(final QueryContext qc, final VarScope scp) throws QueryException {
    final Expr c = super.optimize(qc, scp);
    if (c != this) return c;

    final int es = exprs.length;
    final ExprList list = new ExprList(es);
    for (int i = 0; i < es; i++) {
      Expr e = exprs[i];
      if (e instanceof CmpG) {
        // merge adjacent comparisons
        while (i + 1 < es && exprs[i + 1] instanceof CmpG) {
          final Expr tmp = ((CmpG) e).union((CmpG) exprs[i + 1], qc, scp);
          if (tmp != null) {
            e = tmp;
            i++;
          } else {
            break;
          }
        }
      }
      // expression will always return true
      if (e == Bln.TRUE) return optPre(Bln.TRUE, qc);
      // skip expression yielding false
      if (e != Bln.FALSE) list.add(e);
    }

    // all arguments return false
    if (list.isEmpty()) return optPre(Bln.FALSE, qc);

    if (es != list.size()) {
      qc.compInfo(OPTREWRITE_X, this);
      exprs = list.finish();
    }
    compFlatten(qc);

    boolean not = true;
    for (final Expr expr : exprs) {
      if (!expr.isFunction(Function.NOT)) {
        not = false;
        break;
      }
    }

    if (not) {
      qc.compInfo(OPTREWRITE_X, this);
      final int el = exprs.length;
      final Expr[] inner = new Expr[el];
      for (int e = 0; e < el; e++) inner[e] = ((Arr) exprs[e]).exprs[0];
      final Expr ex = new And(info, inner).optimize(qc, scp);
      return Function.NOT.get(null, info, ex).optimize(qc, scp);
    }

    // return single expression if it yields a boolean
    return exprs.length == 1 ? compBln(exprs[0], info) : this;
  }
Exemple #3
0
 @Override
 public boolean indexAccessible(final IndexInfo ii) throws QueryException {
   int costs = 0;
   final ExprList el = new ExprList(exprs.length);
   for (final Expr expr : exprs) {
     // check if expression can be rewritten, and if access is not sequential
     if (!expr.indexAccessible(ii)) return false;
     // skip expressions without results
     if (ii.costs == 0) continue;
     costs += ii.costs;
     el.add(ii.expr);
   }
   // use summarized costs for estimation
   ii.costs = costs;
   // no expressions means no costs: expression will later be ignored
   ii.expr = el.size() == 1 ? el.get(0) : new Union(info, el.finish());
   return true;
 }