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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5419) Calculate return string length for literals & some string functions
Date Fri, 28 Apr 2017 01:30:04 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15987996#comment-15987996
] 

ASF GitHub Bot commented on DRILL-5419:
---------------------------------------

Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/819#discussion_r113835921
  
    --- 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 --
    
    Why just long?
    
    In general, if we know the input type, we know the maximum output string width for that
type (for all types except, say, Map, List, Repeated, VarBinary.) In many cases, the actual
string won't be the maximum, but at least we set an upper bound far less than the default
of 64K.


> Calculate return string length for literals & some string functions
> -------------------------------------------------------------------
>
>                 Key: DRILL-5419
>                 URL: https://issues.apache.org/jira/browse/DRILL-5419
>             Project: Apache Drill
>          Issue Type: Bug
>    Affects Versions: 1.9.0
>            Reporter: Arina Ielchiieva
>            Assignee: Arina Ielchiieva
>         Attachments: version_with_cast.JPG
>
>
> Though Drill is schema-less and cannot determine in advance what the length of the column
should be but if query has an explicit type/length specified, Drill should return correct
column length.
> For example, JDBC / ODBC Driver is ALWAYS returning 64K as the length of a varchar or
char even if casts are applied.
> Changes:
> *LITERALS*
> String literals length is the same as actual literal length.
> Example: for 'aaa' return length is 3.
> *CAST*
> Return length is the one indicated in cast expression. This also applies when user has
created view where each string columns was casted to varchar with some specific length.
> This length will be returned to the user without need to apply cast one more time. Below
mentioned functions can take leverage of underlying varchar length and calculate return length.
> *LOWER, UPPER, INITCAP, REVERSE, FIRST_VALUE, LAST_VALUE* 
> Return length is underlying column length, i.e. if column is known, the same length will
be returned.
> Example:
> lower(cast(col as varchar(30))) will return 30.
> lower(col) will return max varchar length, since we don't know actual column length.
> *LAG, LEAD*
> Return length is underlying column length but column type will be nullable.
> *LPAD, RPAD*
> Pads the string to the length specified. Return length is this specified length. 
> *CONCAT, CONCAT OPERATOR (||)*
> Return length is sum of underlying columns length. If length is greater then varchar
max length,  varchar max length is returned.
> *SUBSTR, SUBSTRING, LEFT, RIGHT*
> Calculates return length according to each function substring rules, for example, taking
into account how many char should be substracted.
> *IF EXPRESSIONS (CASE STATEMENT, COALESCE), UNION OPERATOR*
> When combining string columns with different length, return length is max from source
columns.



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