@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;
}
@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;
}
@Override
public Expr optimize(final QueryContext qc, final VarScope scp) throws QueryException {
super.optimize(qc, scp);
final ExprList el = new ExprList(exprs.length);
for (final Expr ex : exprs) {
if (ex.isEmpty()) {
// remove empty operands (return empty sequence if first value is empty)
if (el.isEmpty()) return optPre(qc);
qc.compInfo(OPTREMOVE_X_X, this, ex);
} else {
el.add(ex);
}
}
// ensure that results are always sorted
if (el.size() == 1 && iterable) return el.get(0);
// replace expressions with optimized list
exprs = el.finish();
return this;
}
