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From arina-ielchiieva <...@git.apache.org>
Subject [GitHub] drill pull request #819: DRILL-5419: Calculate return string length for lite...
Date Fri, 05 May 2017 12:30:53 GMT
Github user arina-ielchiieva commented on a diff in the pull request:

    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/DrillStringCastFuncHolder.java
    @@ -0,0 +1,56 @@
    + * 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.drill.exec.expr.fn;
    +import com.google.common.primitives.Ints;
    +import org.apache.drill.common.expression.LogicalExpression;
    +import org.apache.drill.common.expression.ValueExpressions;
    +import org.apache.drill.common.types.TypeProtos;
    +import java.util.List;
    + * Function holder for functions with function scope set as
    + * {@link org.apache.drill.exec.expr.annotations.FunctionTemplate.FunctionScope#STRING_CAST}.
    + */
    +public class DrillStringCastFuncHolder extends DrillSimpleFuncHolder {
    +  public DrillStringCastFuncHolder(FunctionAttributes functionAttributes, FunctionInitializer
initializer) {
    +    super(functionAttributes, initializer);
    +  }
    +  /**
    +   * Defines function return type and sets cast length as type precision
    +   * if cast length is simple long expression.
    --- End diff --
    For cast functions we determine output precision by checking second logical expression.
If this expression is passed as long expression (`cast(col as varchar(10)`), then we cast
second logical expression to `ValueExpressions.LongExpression` and  get length value. If customer
has passed length parameter as varchar (`cast(col as varchar('10')`), function will still
work since Drill convert string to long but second expression won't `ValueExpressions.LongExpression`,
it will be `DrillFuncHolder` since cast to bigint would be applied first. In this case it
will be hard to get actual length value (to many checking of instanceof etc). In this case
we leave precision unset. Basically we set precision in cast functions only if user has indicated
cast expression properly.  
    This PR we set precision only for string types, other types are not included.

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