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https://issues.apache.org/jira/browse/NIFI-1706?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16195219#comment-16195219
 ] 

ASF GitHub Bot commented on NIFI-1706:
--------------------------------------

Github user mattyb149 commented on a diff in the pull request:

    https://github.com/apache/nifi/pull/2162#discussion_r143279372
  
    --- Diff: 
nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/QueryDatabaseTable.java
 ---
    @@ -175,6 +181,32 @@ public QueryDatabaseTable() {
             return propDescriptors;
         }
     
    +    @Override
    +    protected Collection<ValidationResult> 
customValidate(ValidationContext validationContext) {
    +        final List<ValidationResult> results = new 
ArrayList<>(super.customValidate(validationContext));
    +
    +        final String tableName = 
validationContext.getProperty(TABLE_NAME).getValue();
    +        final String sqlQuery = 
validationContext.getProperty(SQL_QUERY).getValue();
    +
    +        if(!StringUtils.isEmpty(sqlQuery) && 
!StringUtils.isEmpty(tableName)){
    +            results.add(new ValidationResult.Builder()
    +                        .valid(false)
    +                        .subject("SQL Query")
    +                        .explanation("SQL Query and Table Name can't both 
be specified at the same time.")
    --- End diff --
    
    This might need some elaboration, in case the user wouldn't necessarily 
understand why they can't both be specified (due to EL support in the Table 
Name property, e.g.)


> Extend QueryDatabaseTable to support arbitrary queries
> ------------------------------------------------------
>
>                 Key: NIFI-1706
>                 URL: https://issues.apache.org/jira/browse/NIFI-1706
>             Project: Apache NiFi
>          Issue Type: Improvement
>          Components: Core Framework
>    Affects Versions: 1.4.0
>            Reporter: Paul Bormans
>            Assignee: Peter Wicks
>              Labels: features
>
> The QueryDatabaseTable is able to observe a configured database table for new 
> rows and yield these into the flowfile. The model of an rdbms however is 
> often (if not always) normalized so you would need to join various tables in 
> order to "flatten" the data into useful events for a processing pipeline as 
> can be build with nifi or various tools within the hadoop ecosystem.
> The request is to extend the processor to specify an arbitrary sql query 
> instead of specifying the table name + columns.
> In addition (this may be another issue?) it is desired to limit the number of 
> rows returned per run. Not just because of bandwidth issue's from the nifi 
> pipeline onwards but mainly because huge databases may not be able to return 
> so many records within a reasonable time.



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