void parseOrderColumn(VoltXMLElement orderByNode) {
// make sure everything is kosher
assert (orderByNode.name.equalsIgnoreCase("operation"));
String operationType = orderByNode.attributes.get("type");
assert (operationType != null);
assert (operationType.equalsIgnoreCase("orderby"));
// get desc/asc
String desc = orderByNode.attributes.get("desc");
boolean descending = (desc != null) && (desc.equalsIgnoreCase("true"));
// get the columnref expression inside the orderby node
VoltXMLElement child = orderByNode.children.get(0);
assert (child != null);
// create the orderby column
ParsedColInfo order_col = new ParsedColInfo();
order_col.orderBy = true;
order_col.ascending = !descending;
AbstractExpression order_exp = parseExpressionTree(child);
// Cases:
// inner child could be columnref, in which case it's just a normal
// column. Just make a ParsedColInfo object for it and the planner
// will do the right thing later
if (child.name.equals("columnref")) {
order_col.columnName = child.attributes.get("column");
order_col.tableName = child.attributes.get("table");
String alias = child.attributes.get("alias");
order_col.alias = alias;
// The ORDER BY column MAY be identical to a simple display column, in which case,
// tagging the actual display column as being also an order by column
// helps later when trying to determine ORDER BY coverage (for determinism).
if (order_exp instanceof TupleValueExpression) {
ParsedColInfo orig_col = null;
for (ParsedColInfo col : displayColumns) {
if (col.expression.equals(order_exp)) {
orig_col = col;
break;
}
}
if (orig_col != null) {
orig_col.orderBy = true;
orig_col.ascending = order_col.ascending;
}
}
} else if (child.name.equals("operation")) {
order_col.columnName = "";
// I'm not sure anyone actually cares about this table name
order_col.tableName = "VOLT_TEMP_TABLE";
// If it's a simplecolumn operation. This means that the alias that
// we have should refer to a column that we compute
// somewhere else (like an aggregate, mostly).
// Look up that column in the displayColumns list,
// and then create a new order by column with a magic TVE.
// This case seems to be the result of cross-referencing a display column
// by its position, as in "ORDER BY 2, 3". Otherwise the ORDER BY column
// is a columnref as handled in the prior code block.
if (order_exp instanceof TupleValueExpression) {
String alias = child.attributes.get("alias");
order_col.alias = alias;
ParsedColInfo orig_col = null;
for (ParsedColInfo col : displayColumns) {
if (col.alias.equals(alias)) {
orig_col = col;
break;
}
}
// We need the original column expression so we can extract
// the value size and type for our TVE that refers back to it.
// XXX: This check runs into problems for some cases where a display column expression gets
// re-used in the ORDER BY.
// I THINK one problem case was "select x, max(y) from t group by x order by max(y);" --paul
if (orig_col == null) {
throw new PlanningErrorException(
"Unable to find source " + "column for simplecolumn: " + alias);
}
// Tagging the actual display column as being also an order by column
// helps later when trying to determine ORDER BY coverage (for determinism).
orig_col.orderBy = true;
orig_col.ascending = order_col.ascending;
assert (orig_col.tableName.equals("VOLT_TEMP_TABLE"));
// Construct our fake TVE that will point back at the input
// column.
TupleValueExpression tve = (TupleValueExpression) order_exp;
tve.setColumnAlias(alias);
tve.setColumnName("");
tve.setColumnIndex(-1);
tve.setTableName("VOLT_TEMP_TABLE");
tve.setValueSize(orig_col.expression.getValueSize());
tve.setValueType(orig_col.expression.getValueType());
if (orig_col.expression.hasAnySubexpressionOfClass(AggregateExpression.class)) {
tve.setHasAggregate(true);
}
}
} else if (child.name.equals("function") == false) {
throw new RuntimeException("ORDER BY parsed with strange child node type: " + child.name);
}
if (order_exp instanceof ConstantValueExpression) {
assert (order_exp.getValueType() != VoltType.NUMERIC);
}
ExpressionUtil.finalizeValueTypes(order_exp);
order_col.expression = order_exp;
orderColumns.add(order_col);
}
