[jira] [Commented] (FLINK-6891) Add LOG(X) supported in SQL

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-6891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16060808#comment-16060808 ] 

ASF GitHub Bot commented on FLINK-6891:
---------------------------------------

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

    https://github.com/apache/flink/pull/4122#discussion_r123734574
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/runtime/scalarfunctions/MathScalarFunctions.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.runtime.scalarfunctions
    +
    +/**
    +  * All build-in math scalar functions.
    +  */
    +class MathScalarFunctions {}
    +
    +object MathScalarFunctions {
    +  /**
    +    * Returns the natural logarithm of "x".
    +    */
    +  def log(x: Double): Double = {
    --- End diff --
    
    Can't we just use the `Math.log` as the built in method? It would reduce complexity as we would not need a CallGenerator then.


> Add LOG(X) supported in SQL
> ---------------------------
>
>                 Key: FLINK-6891
>                 URL: https://issues.apache.org/jira/browse/FLINK-6891
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Table API & SQL
>    Affects Versions: 1.4.0
>            Reporter: sunjincheng
>            Assignee: sunjincheng
>
> LOG(X), LOG(B,X)
> If called with one parameter, this function returns the natural logarithm of X. If X is less than or equal to 0.0E0, the function returns NULL and (as of MySQL 5.7.4) a warning “Invalid argument for logarithm” is reported.
> The inverse of this function (when called with a single argument) is the EXP() function.
> If called with two parameters, this function returns the logarithm of X to the base B. If X is less than or equal to 0, or if B is less than or equal to 1, then NULL is returned.
> * Example:
>  LOG(2) -> 0.69314718055995
>  LOG(-2) -> NULL
>  LOG(2,65536) -> 16
>  LOG(10,100) -> 2
>  LOG(1,100) -> NULL
> * See more:
> ** [MySQL| https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_log]
> --NOTE-- In this JIRA. NULL case will throw IllegalArgumentException.



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