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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5566) Introduce structure to hold table and column level statistics
Date Tue, 14 Feb 2017 02:49:41 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5566?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15864928#comment-15864928
] 

ASF GitHub Bot commented on FLINK-5566:
---------------------------------------

Github user beyond1920 commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3196#discussion_r100950729
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/stats/ColumnStats.scala
---
    @@ -0,0 +1,52 @@
    +/*
    + * 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.flink.table.plan.stats
    +
    +/**
    +  * column statistics
    +  *
    +  * @param ndv       number of distinct values
    +  * @param nullCount number of nulls
    +  * @param avgLen    average length of column values
    +  * @param maxLen    max length of column values
    +  * @param max       max value of column values
    +  * @param min       min value of column values
    +  */
    +case class ColumnStats(
    +    ndv: Long,
    --- End diff --
    
    @fhueske , there is no need to make all stats optional. If there is no statistics for
ndv/nullcount/avgLen/maxLen, we could give them an invalid value, e.g, -1. But it does not
work for max/min, because max/min value could be possible negative. 


> Introduce structure to hold table and column level statistics
> -------------------------------------------------------------
>
>                 Key: FLINK-5566
>                 URL: https://issues.apache.org/jira/browse/FLINK-5566
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Table API & SQL
>            Reporter: Kurt Young
>            Assignee: zhangjing
>
> We define two structure mode to hold statistics
> 1. TableStats: contain stats for table level, now only one element: rowCount
> 2. ColumnStats: contain stats of column level. 
> for numeric column type: including ndv, nullCount, max, min, histogram
> for string type: including ndv, nullCount, avgLen,maxLen
> for boolean:including ndv, nullCount, trueCount, falseCount
> for date/time/timestamp:  including ndv, nullCount, max, min, histogram 



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