/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.tajo.engine.planner;
import org.apache.tajo.algebra.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
/**
* ExprNormalizer performs two kinds of works:
*
* <h3>1. Duplication Removal.</h3>
*
* For example, assume a simple query as follows:
* <pre>
* select price * rate as total_price, ..., order by price * rate
* </pre>
*
* The expression <code>price * rate</code> is duplicated in both select list and order by clause.
* Against those cases, ExprNormalizer removes duplicated expressions and replaces one with one reference.
* In the case, ExprNormalizer replaces price * rate with total_price reference.
*
* <h3>2. Dissection of Expression</h3>
*
* A expression can be a complex expressions, including a mixed of scalar and aggregation expressions.
* For example, assume an aggregation query as follows:
* <pre>
* select sum(price * rate) * (1 - avg(discount_rate))), ...
* </pre>
*
* In this case, ExprNormalizer dissects the expression 'sum(price * rate) * (1 - avg(discount_rate)))'
* into the following expressions:
* <ul>
* <li>$1 = price * rage</li>
* <li>$2 = sum($1)</li>
* <li>$3 = avg(discount_rate)</li>
* <li>$4 = $2 * (1 - $3)</li>
* </ul>
*
* It mainly two advantages. Firstly, it makes complex expression evaluations easier across multiple physical executors.
* Second, it gives move opportunities to remove duplicated expressions.
*
* <h3>3. Name Normalization</h3>
*
* Users can use qualified column names, unqualified column names or aliased column references.
*
* Consider the following example:
*
* <pre>
* select rate_a as total_rate, rate_a * 100, table1.rate_a, ... WHERE total_rate * 100
* </pre>
*
* <code>total_rate</code>, <code>rate_a</code>, and <code>table1.rate_a</code> are all the same references. But,
* they have different forms. Due to their different forms, duplication removal can be hard.
*
* In order to solve this problem, ExprNormalizer normalizes all column references as qualified names while it keeps
* its points..
*/
class ExprNormalizer extends SimpleAlgebraVisitor<ExprNormalizer.ExprNormalizedResult, Object> {
public static class ExprNormalizedResult {
private final LogicalPlan plan;
private final LogicalPlan.QueryBlock block;
Expr baseExpr; // outmost expressions, which can includes one or more references of the results of aggregation
// function.
List<NamedExpr> aggExprs = new ArrayList<NamedExpr>(); // aggregation functions
List<NamedExpr> scalarExprs = new ArrayList<NamedExpr>(); // scalar expressions which can be referred
private ExprNormalizedResult(LogicalPlanner.PlanContext context) {
this.plan = context.plan;
this.block = context.queryBlock;
}
@Override
public String toString() {
return baseExpr.toString() + ", agg=" + aggExprs.size() + ", scalar=" + scalarExprs.size();
}
}
public ExprNormalizedResult normalize(LogicalPlanner.PlanContext context, Expr expr) throws PlanningException {
ExprNormalizedResult exprNormalizedResult = new ExprNormalizedResult(context);
Stack<Expr> stack = new Stack<Expr>();
stack.push(expr);
visit(exprNormalizedResult, new Stack<Expr>(), expr);
exprNormalizedResult.baseExpr = stack.pop();
return exprNormalizedResult;
}
@Override
public Object visitCaseWhen(ExprNormalizedResult ctx, Stack<Expr> stack, CaseWhenPredicate expr)
throws PlanningException {
stack.push(expr);
for (CaseWhenPredicate.WhenExpr when : expr.getWhens()) {
visit(ctx, stack, when.getCondition());
visit(ctx, stack, when.getResult());
if (OpType.isAggregationFunction(when.getCondition().getType())) {
String referenceName = ctx.block.namedExprsMgr.addExpr(when.getCondition());
ctx.aggExprs.add(new NamedExpr(when.getCondition(), referenceName));
when.setCondition(new ColumnReferenceExpr(referenceName));
}
if (OpType.isAggregationFunction(when.getResult().getType())) {
String referenceName = ctx.block.namedExprsMgr.addExpr(when.getResult());
ctx.aggExprs.add(new NamedExpr(when.getResult(), referenceName));
when.setResult(new ColumnReferenceExpr(referenceName));
}
}
if (expr.hasElseResult()) {
visit(ctx, stack, expr.getElseResult());
if (OpType.isAggregationFunction(expr.getElseResult().getType())) {
String referenceName = ctx.block.namedExprsMgr.addExpr(expr.getElseResult());
ctx.aggExprs.add(new NamedExpr(expr.getElseResult(), referenceName));
expr.setElseResult(new ColumnReferenceExpr(referenceName));
}
}
stack.pop();
return expr;
}
@Override
public Expr visitUnaryOperator(ExprNormalizedResult ctx, Stack<Expr> stack, UnaryOperator expr) throws PlanningException {
super.visitUnaryOperator(ctx, stack, expr);
if (OpType.isAggregationFunction(expr.getChild().getType())) {
// Get an anonymous column name and replace the aggregation function by the column name
String refName = ctx.block.namedExprsMgr.addExpr(expr.getChild());
ctx.aggExprs.add(new NamedExpr(expr.getChild(), refName));
expr.setChild(new ColumnReferenceExpr(refName));
}
return expr;
}
@Override
public Expr visitBinaryOperator(ExprNormalizedResult ctx, Stack<Expr> stack, BinaryOperator expr) throws PlanningException {
super.visitBinaryOperator(ctx, stack, expr);
////////////////////////
// For Left Term
////////////////////////
if (OpType.isAggregationFunction(expr.getLeft().getType())) {
String leftRefName = ctx.block.namedExprsMgr.addExpr(expr.getLeft());
ctx.aggExprs.add(new NamedExpr(expr.getLeft(), leftRefName));
expr.setLeft(new ColumnReferenceExpr(leftRefName));
}
////////////////////////
// For Right Term
////////////////////////
if (OpType.isAggregationFunction(expr.getRight().getType())) {
String rightRefName = ctx.block.namedExprsMgr.addExpr(expr.getRight());
ctx.aggExprs.add(new NamedExpr(expr.getRight(), rightRefName));
expr.setRight(new ColumnReferenceExpr(rightRefName));
}
return expr;
}
///////////////////////////////////////////////////////////////////////////////////////////////////////////
// Function Section
///////////////////////////////////////////////////////////////////////////////////////////////////////////
@Override
public Expr visitFunction(ExprNormalizedResult ctx, Stack<Expr> stack, FunctionExpr expr) throws PlanningException {
stack.push(expr);
Expr param;
for (int i = 0; i < expr.getParams().length; i++) {
param = expr.getParams()[i];
visit(ctx, stack, param);
if (OpType.isAggregationFunction(param.getType())) {
String referenceName = ctx.plan.generateUniqueColumnName(param);
ctx.aggExprs.add(new NamedExpr(param, referenceName));
expr.getParams()[i] = new ColumnReferenceExpr(referenceName);
}
}
stack.pop();
return expr;
}
@Override
public Expr visitGeneralSetFunction(ExprNormalizedResult ctx, Stack<Expr> stack, GeneralSetFunctionExpr expr)
throws PlanningException {
stack.push(expr);
Expr param;
for (int i = 0; i < expr.getParams().length; i++) {
param = expr.getParams()[i];
visit(ctx, stack, param);
// If parameters are all constants, we don't need to dissect an aggregation expression into two parts:
// function and parameter parts.
if (!OpType.isLiteral(param.getType())) {
String referenceName = ctx.block.namedExprsMgr.addExpr(param);
ctx.scalarExprs.add(new NamedExpr(param, referenceName));
expr.getParams()[i] = new ColumnReferenceExpr(referenceName);
}
}
stack.pop();
return expr;
}
///////////////////////////////////////////////////////////////////////////////////////////////////////////
// Literal Section
///////////////////////////////////////////////////////////////////////////////////////////////////////////
@Override
public Expr visitCastExpr(ExprNormalizedResult ctx, Stack<Expr> stack, CastExpr expr) throws PlanningException {
super.visitCastExpr(ctx, stack, expr);
if (OpType.isAggregationFunction(expr.getType())) {
String referenceName = ctx.block.namedExprsMgr.addExpr(expr.getChild());
ctx.aggExprs.add(new NamedExpr(expr.getChild(), referenceName));
expr.setChild(new ColumnReferenceExpr(referenceName));
}
return expr;
}
@Override
public Expr visitColumnReference(ExprNormalizedResult ctx, Stack<Expr> stack, ColumnReferenceExpr expr)
throws PlanningException {
// normalize column references.
if (!expr.hasQualifier()) {
if (ctx.block.namedExprsMgr.contains(expr.getCanonicalName())) {
NamedExpr namedExpr = ctx.block.namedExprsMgr.getNamedExpr(expr.getCanonicalName());
return new ColumnReferenceExpr(namedExpr.getAlias());
} else {
String normalized = ctx.plan.getNormalizedColumnName(ctx.block, expr);
expr.setName(normalized);
}
}
return expr;
}
}