public override Table VisitWhere_clause(QueryParser.Where_clauseContext context)
{
var result = new Table(_table);
foreach (var row in _table)
{
var env = new Environment(row, _table.Columns);
var value = new CondExprVisitor(_zmi, env).Visit(context.cond_expr());
if (value.HasValue && value.Val.Value.GetBoolean())
result.AppendRow(row);
}
return result;
}
public override Maybe<QueryResult> VisitSel_item(QueryParser.Sel_itemContext context)
{
var distinct = context.sel_modifier()?.DISTINCT() != null;
var alias = context.identifier();
var dict = new Dictionary<Attribute, List<Value>>();
foreach (var son in _zmi.Sons)
{
foreach (var (k, v) in son.Attributes)
{
if (dict.TryGetValue(k, out var l))
l.Add(v);
else
dict.Add(k, new List<Value> {v});
}
}
var (attributes, values) = _table.Columns
.Where(c => !Attribute.IsQuery(c))
.Select(c => (key: c, value: _table.GetColumn(c)))
.ToList()
.Unzip(pair => pair.key, pair => pair.value);
var env = new Environment(
new TableRow(values.Select(list =>
list.IsNull || ((AttributeTypeCollection) list.AttributeType).ElementType ==
AttributeTypePrimitive.Null
? ValueNull.Instance as Value
: list)), attributes, true);
var result = new CondExprVisitor(_zmi, env).Visit(context.cond_expr());
return result.Bind(res =>
{
switch (res)
{
case ResultSingle _:
break;
default:
throw new ArgumentException("Could not return result which is not aggregated");
}
return alias == null
? new QueryResult(res.Value).Just()
: new QueryResult(new Attribute(alias.GetText()), res.Value).Just();
});
}
public override Table VisitOrder_item(QueryParser.Order_itemContext context)
{
int Comparer(TableRow row1, TableRow row2)
{
var env1 = new Environment(row1, _table.Columns);
var expr1 = new CondExprVisitor(_zmi, env1).Visit(context.cond_expr());
var env2 = new Environment(row2, _table.Columns);
var expr2 = new CondExprVisitor(_zmi, env2).Visit(context.cond_expr());
var result = expr1.Zip(expr2).Bind(p =>
{
var res = new NullsVisitor(p).VisitNulls(context.nulls());
if (res == 0)
return new OrderVisitor(p).VisitOrder(context.order()).Just();
return res.Just();
});
return result.Match(i => i, () => 0);
}
_table.Sort(Compare.By<TableRow>(Comparer));
return _table;
}
