static FarragoSession getSession(RelNode rel) { FarragoSessionPlanner planner = (FarragoSessionPlanner) rel.getCluster().getPlanner(); FarragoSessionPreparingStmt preparingStmt = planner.getPreparingStmt(); return preparingStmt.getSession(); }
/** * Reduces a list of expressions. * * @param rel Relational expression * @param expList List of expressions, modified in place * @return whether reduction found something to change, and succeeded */ static boolean reduceExpressions(RelNode rel, List<RexNode> expList) { RexBuilder rexBuilder = rel.getCluster().getRexBuilder(); // Find reducible expressions. FarragoSessionPlanner planner = (FarragoSessionPlanner) rel.getCluster().getPlanner(); FarragoSessionPreparingStmt preparingStmt = planner.getPreparingStmt(); List<RexNode> constExps = new ArrayList<RexNode>(); List<Boolean> addCasts = new ArrayList<Boolean>(); List<RexNode> removableCasts = new ArrayList<RexNode>(); findReducibleExps(preparingStmt, expList, constExps, addCasts, removableCasts); if (constExps.isEmpty() && removableCasts.isEmpty()) { return false; } // Remove redundant casts before reducing constant expressions. // If the argument to the redundant cast is a reducible constant, // reducing that argument to a constant first will result in not being // able to locate the original cast expression. if (!removableCasts.isEmpty()) { List<RexNode> reducedExprs = new ArrayList<RexNode>(); List<Boolean> noCasts = new ArrayList<Boolean>(); for (RexNode exp : removableCasts) { RexCall call = (RexCall) exp; reducedExprs.add(call.getOperands()[0]); noCasts.add(false); } RexReplacer replacer = new RexReplacer(rexBuilder, removableCasts, reducedExprs, noCasts); replacer.apply(expList); } if (constExps.isEmpty()) { return true; } // Compute the values they reduce to. List<RexNode> reducedValues = new ArrayList<RexNode>(); ReentrantValuesStmt reentrantStmt = new ReentrantValuesStmt( preparingStmt.getRootStmtContext(), rexBuilder, constExps, reducedValues); FarragoSession session = getSession(rel); reentrantStmt.execute(session, true); if (reentrantStmt.failed) { return false; } // For ProjectRel, we have to be sure to preserve the result // types, so always cast regardless of the expression type. // For other RelNodes like FilterRel, in general, this isn't necessary, // and the presence of casts could hinder other rules such as sarg // analysis, which require bare literals. But there are special cases, // like when the expression is a UDR argument, that need to be // handled as special cases. if (rel instanceof ProjectRel) { for (int i = 0; i < reducedValues.size(); i++) { addCasts.set(i, true); } } RexReplacer replacer = new RexReplacer(rexBuilder, constExps, reducedValues, addCasts); replacer.apply(expList); return true; }