[jira] [Commented] (FLINK-26945) Add DATE_SUB supported in SQL & Table API

["jackylau (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-26945?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17694857#comment-17694857 ] 

jackylau commented on FLINK-26945:
----------------------------------

i think it is not good. because the numDays is limit to day. i suggest use bigquery style in calcite. 
{code:java}
// code placeholder
public static final SqlFunction DATE_SUB =
    SqlBasicFunction.create(SqlKind.DATE_SUB, ReturnTypes.ARG0_NULLABLE,
         OperandTypes.DATE_INTERVAL)
        .withFunctionType(SqlFunctionCategory.TIMEDATE); {code}
like this 

 SELECT DATE_SUB('2018-05-01',INTERVAL 1 YEAR/MONTH/DAY);  -> '2017-05-01'

 

> Add DATE_SUB supported in SQL & Table API
> -----------------------------------------
>
>                 Key: FLINK-26945
>                 URL: https://issues.apache.org/jira/browse/FLINK-26945
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Table SQL / API
>            Reporter: dalongliu
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.17.0
>
>
> Returns the date {{numDays}} before {{{}startDate{}}}.
> Syntax:
> {code:java}
> date_sub(startDate, numDays) {code}
> Arguments:
>  * {{{}startDate{}}}: A DATE expression.
>  * {{{}numDays{}}}: An INTEGER expression.
> Returns:
> A DATE.
> If {{numDays}} is negative abs(num_days) are added to {{{}startDate{}}}.
> If the result date overflows the date range the function raises an error.
> Examples:
> {code:java}
> > SELECT date_sub('2016-07-30', 1);
>  2016-07-29 {code}
> See more:
>  * [Spark|https://spark.apache.org/docs/latest/sql-ref-functions-builtin.html#date-and-timestamp-functions]
>  * [Hive|https://cwiki.apache.org/confluence/display/hive/languagemanual+udf]



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