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From Yohann Lepage <>
Subject Re: ExecuteSQL question
Date Wed, 03 Aug 2016 14:34:12 GMT

I have exactly the same use case to periodically get rows from some
security appliances with just a read only access.

Currently (without NiFi), we use an SQL query  to track the maximum
value, depending on the DB/appliance/vendor, it could be a simple
"SELECT getdate()" or  "select max(SW_TIME) from log_table" or  a more
complex query with INNER JOIN.

So, it would be great to have an option to customize the tracking query.


2016-08-03 16:02 GMT+02:00 Conrad Crampton <>:
> Hi,
> Thanks for this.
> I did think about a MV but unfortunately I haven’t access to create views – just
read access. That would have been my simplest option ;-) Life’s never that easy though is
> The only part of the sql I need to be dynamic is the date parameter (I could even use
the id column). Instead of using the MapCache (if that isn’t a good idea), could I use the
GetFile to just pull a single txt file with the parameter (i.e. last run or max id value from
the last run), which creates flowfile, read that value and pass that into ExecuteSql (using
the aforementioned value as the parameter in the sql) as the select query can be dynamically
constructed from attributes/ flowfile content (as per docs)? And then finally write text file
back to file system to be picked up next time?
> Thanks
> Conrad
> On 03/08/2016, 14:02, "Matt Burgess" <> wrote:
>     Conrad,
>     Is it possible to add a view (materialized or not) to the RDBMS? That
>     view could take care of the denormalization and then
>     QueryDatabaseTable could point at the view. The DB would take care of
>     the push-down filters, which functionally is like if you had a
>     QueryDatabaseTable for each table then did the joins.
>     In NiFi 1.0 there is a GenerateTableFetch processor which is like
>     QueryDatabaseTable except it generates SQL instead of executing SQL.
>     That might be used in your a) option above but you'd have to reconcile
>     the SQL statements into a JOIN. A possible improvement to either/both
>     processors would be to add attributes for the maximum value columns
>     whose values are the maximum observed values. Then you wouldn't have
>     to parse or manipulate the SQL if you really just want the max values.
>     I have been thinking about how QueryDatabaseTable and
>     GenerateTableFetch would work if they accepted incoming flow files (to
>     allow dynamic table names for example). It's a bit more tricky because
>     those processors run without input to get max values, so their
>     behavior would change when a flow file is present but would return to
>     the original behavior if no flow file is present. Since the
>     ListDatabaseTables processor is also in 1.0, it would be nice to use
>     that as input to the other two processors.
>     I'm definitely interested in any thoughts or discussion around these things :)
>     Regards,
>     Matt
>     On Wed, Aug 3, 2016 at 8:37 AM, Conrad Crampton
>     <> wrote:
>     > Hi,
>     >
>     > My use case is that I want to ship a load of rows from an RDMS periodically
>     > and put in HDFS as Avro.
>     >
>     > QueryTable processor has functionality that would be great i.e. maxcolumn
>     > value (there are couple of columns I could use for this from the data) and
>     > it is this functionality I am looking for, BUT the data is not from one
>     > single table. The nature of the RDBMS is that the business view on the data
>     > requires a bunch of joins from other tables/schemas to get the correct Avro
>     > file so the options I appear to have are
>     >
>     > a)       Use QueryTable for each table that make up the business view and do
>     > the joins etc. in HDFS (Spark or something) – or potentially do the
>     > reconciliation within NiFi???
>     >
>     > b)       Use ExecuteSQL to run the complete SQL to get the rows which can
>     > easily be put into HDFS as Avro given that the line will be the business
>     > (denormalised) data that is required.
>     >
>     > The problem with a) is the reconciliation (denormalisation) of the data and
>     > the problem with b) is how to maintain the maxcolumn value so I only get the
>     > data since the last run.
>     >
>     >
>     >
>     > In order to address b) can I use the DistrubutedMapCacheServer & Client
>     > hold a key/value pair of last run date and extract from this date as a
>     > parameter?
>     >
>     >
>     >
>     > Thanks for any suggestions.
>     >
>     >
>     >
>     > Conrad
>     >
>     >
>     >
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Yohann Lepage

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