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https://issues.apache.org/jira/browse/FLINK-5566?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15865033#comment-15865033
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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_r100958745
--- 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,
+ nullCount: Long,
+ avgLen: Long,
+ maxLen: Long,
+ max: Option[Any],
+ min: Option[Any]) {
--- End diff --
It makes sense to add a field to denote whether stats are precise or
approximate and a field to hold timestamp when the stats were generated. But
I'm not sure how these two fields effects the optimized plan. Because we prefer
to use the provided stats, even it is estimated value or it is a little stale.
So I didn't add these two fields currently, maybe will add them later. What do
you think?
> 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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