hum it sounds not easy to implement, at least for me because it requires
significant changes in Select / Parser.
in the meantime, I have finished a first working implementation which
builds a new query by picking elements from the main request. The main
drawback is that the query is built in text and then reparsed. This looks
like this:
public class Rank extends Expression {
...
public Rank(Select mainSelect, ArrayList<Expression> partitions,
ArrayList<SelectOrderBy> rankOrderList, boolean dense) {
...
}
private Prepared buildRankSelect(Session session) {
// build rank map select
StatementBuilder sb = new StatementBuilder();
sb.append("SELECT ");
sb.resetCount();
for (Expression e : partitions) {
sb.appendExceptFirst(",");
sb.append(e.getSQL());
}
for (SelectOrderBy o : rankOrderList) {
sb.appendExceptFirst(",");
sb.append(o.expression.getSQL());
}
sb.append(" FROM ");
TableFilter filter = mainSelect.getTopTableFilter();
if (filter != null) {
sb.resetCount();
int i = 0;
do {
sb.appendExceptFirst(" ");
sb.append(filter.getPlanSQL(i++ > 0));
filter = filter.getJoin();
} while (filter != null);
} else {
sb.resetCount();
int i = 0;
for (TableFilter f : mainSelect.getTopFilters()) {
do {
sb.appendExceptFirst(" ");
sb.append(f.getPlanSQL(i++ > 0));
f = f.getJoin();
} while (f != null);
}
}
if (mainSelect.getCondition() != null) {
sb.append(" WHERE ").append(
StringUtils.unEnclose(mainSelect.getCondition().getSQL()));
}
sb.append(" ORDER BY ");
sb.resetCount();
for (Expression e : partitions) {
sb.appendExceptFirst(",");
sb.append(StringUtils.unEnclose(e.getSQL()));
}
for (SelectOrderBy o : rankOrderList) {
sb.appendExceptFirst(",");
sb.append(StringUtils.unEnclose(o.getSQL()));
}
System.out.println("SQL=" + sb.toString());
// execute
Parser parser = new Parser(session);
return parser.prepare(sb.toString());
}
on the good side, it works without changes to H2 classes. I've tested it
successfully in my project where I execute Oracle requests in H2 based unit
tests.
what do you think? is it too "hackish"? or am I missing something?
I can provide a complete patch if you want.
BTW, I have difficulties when I execute H2 tests with 'build test': some tests
generate error messages and when I reach testIndex, it just runs forever.
Boris.
Le dimanche 17 juillet 2016 21:25:25 UTC+2, Noel Grandin a écrit :
>
> I think you're going to need to run your new query before the main select
> and then re-init the main select
>
> Running it on-demand like that is going to lead to it trying to run
> somewhere inside the main select and confusing things.
>
> Which means that the top-level select code will probably have to somewhere
> do an explicit walk over the tree to run RANK-type queries, but that is
> fine, I always assumed that RANK-type stuff would need special handling at
> the top level.
>
>
>
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