Hi Mike, Let me answer your question with some queries: >>> select * from dfs.test.`record.json`; +----------------------------------------------------------------------------------+ | record | +----------------------------------------------------------------------------------+ | [{"a":{"a1":5.0,"a2":6.0},"b":{}},{"a":{},"b":{"b1":55.0,"b2":66.0,"b3":77.0}},{"a":{"a1":7.0,"a2":8.0},"b":{}},{"a":{},"b":{"b1":77.0,"b2":88.0,"b3":99.0}}] | +----------------------------------------------------------------------------------+
Now... I can flatten that like this: >>> select flatten(record) AS data from dfs.test.`record.json`; +----------------------------------------------+ | data | +----------------------------------------------+ | {"a":{"a1":5.0,"a2":6.0},"b":{}} | | {"a":{},"b":{"b1":55.0,"b2":66.0,"b3":77.0}} | | {"a":{"a1":7.0,"a2":8.0},"b":{}} | | {"a":{},"b":{"b1":77.0,"b2":88.0,"b3":99.0}} | +----------------------------------------------+ 4 rows selected (0.298 seconds) You asked about filtering. For this, I broke it up into a subquery, but here's how I did that: >>> SELECT data['a'], data['b'] 2..semicolon> FROM (select flatten(record) AS data from dfs.test.`record.json`) 3..semicolon> WHERE data['b']['b1'] > 60.0; +--------+---------------------------------+ | EXPR$0 | EXPR$1 | +--------+---------------------------------+ | {} | {"b1":77.0,"b2":88.0,"b3":99.0} | +--------+---------------------------------+ 1 row selected (0.379 seconds) I did all this without the union data type. Does this make sense? Best, -- C > On Sep 13, 2023, at 11:08 AM, Mike Beckerle <mbecke...@apache.org> wrote: > > I'm thinking whether a first prototype of DFDL integration to Drill should > just use JSON. > > But please consider this JSON: > > { "record": [ > { "a": { "a1":5, "a2":6 } }, > { "b": { "b1":55, "b2":66, "b3":77 } } > { "a": { "a1":7, "a2":8 } }, > { "b": { "b1":77, "b2":88, "b3":99 } } > ] } > > It corresponds to this text data file, parsed using Daffodil: > > 105062556677107082778899 > > The file is a stream of records. The first byte is a tag value 1 for type > 'a' records, and 2 for type 'b' records. > The 'a' records are 2 fixed length fields, each 2 bytes long, named a1 and > a2. They are integers. > The 'b' records are 3 fixed length fields, each 2 bytes long, named b1, b2, > and b3. They are integers. > This kind of format is very common, even textualized like this (from COBOL > programs for example) > > Can Drill query the JSON above to get (b1, b2) where b1 > 10 ? > (and ... does this require the experimental Union feature?) > > b1, b2 > --------- > (55, 66) > (77, 88) > > I ask because in an XML Schema or DFDL schema choices with dozens of > 'branches' are very common. > Ex: schema for the above data: > > <element name="record" maxOccurs="unbounded"> > <complexType> > <choice><!-- there are sub-record types, a, b,... there could be many > dozens of these --> > <element name="a"> > <complexType> > <sequence> > ... many child elements let's say named a1, a2, ... > </sequence> > </complexType> > </element> > <element name="b"> > <complexType> > <sequence> > ... many child elements let's say named b1, b2, b3 > ... > </sequence> > </complexType> > </element> > </choice> > </complexType> > </element> > > To me XSD choice naturally requires a Union feature of some sort. > If that's expermental still in Drill ... what to do? > > On Sun, Aug 6, 2023 at 10:19 AM Charles S. Givre <notificati...@github.com> > wrote: > >> @mbeckerle <https://github.com/mbeckerle> >> You've encountered another challenge that exists in Drill reading data >> without a schema. >> Let me explain a bit about this and I'm going to use the JSON reader as an >> example. First Drill requires data to be homogeneous. Drill does have a >> Union vector type which allows heterogeneous data however this is a bit >> experimental and I wouldn't recommend using it. Also, it really just shifts >> schema inconsistencies to the user. >> >> For instance, let's say you have a column consisting of strings and >> floats. What happens if you try to do something like this: >> >> SELECT sum(mixed_col)-- orSELECT.... ORDER BY mixed_col >> >> Remembering that Drill is distributed and if you have a column with the >> same name and you try to do these operations, they will fail. >> >> Let's say we have data like this: >> >> [ >> { >> 'col1': 'Hi there', >> 'col2': 5.0 >> }, >> { >> 'col1':True, >> 'col2': 4, >> 'col3': 'foo' >> } >> ] >> >> In older versions of Drill, this kind of data, this would throw all kinds >> of SchemaChangeExceptions. However, in recent versions of Drill, @jnturton >> <https://github.com/jnturton> submitted apache#2638 >> <https://github.com/apache/drill/pull/2638> which overhauled implicit >> casting. What this meant for users is that col2 in the above would be >> automatically cast to a FLOAT and col1 would be automatically cast to a >> VARCHAR. >> >> However, when reading data the story is a little different. What we did >> for the JSON reader was have several read modes. The least tolerant >> attempts to infer all data types. This seems like a great idea in practice, >> however when you start actually using Drill with real data, you start >> seeing the issues with this approach. The JSON reader has a few >> configuration options that increase its tolerance for bad data. The next >> level is readAllNumbersAsDouble which... as the name implies, reads all >> numeric data as Doubles and does not attempt to infer ints vs floats. The >> next options is allTextMode which reads all fields as VARCHAR. This >> should be used when the data is so inconsistent that it cannot be read with >> either mode. These modes can be set globally, at the plugin level or at >> query time. >> >> For the XML reader, I didn't add type inference because I figured the data >> would be quite messy, however it wouldn't be that hard to add basically the >> same levels as the JSON reader. >> >> This fundamental issue exists in all the readers that read data without a >> schema. My rationale for working on the XSD reader is that this will enable >> us to accurately read XML data with all the correct data types. >> >> — >> Reply to this email directly, view it on GitHub >> <https://github.com/cgivre/drill/pull/6#issuecomment-1666875922>, or >> unsubscribe >> <https://github.com/notifications/unsubscribe-auth/AALUDAZZ6T6Z44AW44IKD2LXT6RVNANCNFSM6AAAAAA26ZZVQ4> >> . >> You are receiving this because you were mentioned.Message ID: >> <cgivre/drill/pull/6/c1666875...@github.com> >>