| // 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.impala.rewrite; |
| |
| import org.apache.impala.analysis.Analyzer; |
| import org.apache.impala.analysis.CastExpr; |
| import org.apache.impala.analysis.Expr; |
| import org.apache.impala.analysis.LiteralExpr; |
| import org.apache.impala.common.AnalysisException; |
| |
| /** |
| * This rule replaces a constant Expr with its equivalent LiteralExpr by evaluating the |
| * Expr in the BE. Exprs that are already LiteralExprs are not changed. |
| * |
| * TODO: Expressions fed into this rule are currently not required to be analyzed |
| * in order to support constant folding in expressions that contain unresolved |
| * references to select-list aliases (such expressions cannot be analyzed). |
| * The cross-dependencies between rule transformations and analysis are vague at the |
| * moment and make rule application overly complicated. |
| * |
| * Examples: |
| * 1 + 1 + 1 --> 3 |
| * toupper('abc') --> 'ABC' |
| * cast('2016-11-09' as timestamp) --> TIMESTAMP '2016-11-09 00:00:00' |
| */ |
| public class FoldConstantsRule implements ExprRewriteRule { |
| public static ExprRewriteRule INSTANCE = new FoldConstantsRule(); |
| |
| @Override |
| public Expr apply(Expr expr, Analyzer analyzer) throws AnalysisException { |
| // Avoid calling Expr.isConstant() because that would lead to repeated traversals |
| // of the Expr tree. Assumes the bottom-up application of this rule. Constant |
| // children should have been folded at this point. |
| for (Expr child: expr.getChildren()) if (!Expr.IS_LITERAL.apply(child)) return expr; |
| if (Expr.IS_LITERAL.apply(expr) || !expr.isConstant()) return expr; |
| |
| // Do not constant fold cast(null as dataType) because we cannot preserve the |
| // cast-to-types and that can lead to query failures, e.g., CTAS |
| if (expr instanceof CastExpr) { |
| CastExpr castExpr = (CastExpr) expr; |
| if (Expr.IS_NULL_LITERAL.apply(castExpr.getChild(0))) { |
| return expr; |
| } |
| } |
| // Analyze constant exprs, if necessary. Note that the 'expr' may become non-constant |
| // after analysis (e.g., aggregate functions). |
| if (!expr.isAnalyzed()) { |
| expr.analyze(analyzer); |
| if (!expr.isConstant()) return expr; |
| } |
| Expr result = LiteralExpr.createBounded(expr, analyzer.getQueryCtx(), |
| LiteralExpr.MAX_STRING_LITERAL_SIZE); |
| |
| // Preserve original type so parent Exprs do not need to be re-analyzed. |
| if (result != null) return result.castTo(expr.getType()); |
| return expr; |
| } |
| |
| private FoldConstantsRule() {} |
| } |