Hi, when you create a structure type, you should choose StructKind.PEEK_FIELDS instead, which let you to access the nested fields with DOT, i.e. “a.b.c”.
Best, Danny Chan 在 2020年6月16日 +0800 AM4:21，Slim Bouguerra <bs...@apache.org>，写道： > I am using this thread since the question seems related. > As of now I can not say a way to project a nested record (FYI scalar > works). https://jira.apache.org/jira/browse/CALCITE-4065 > @Igor any idea if this can be done without major work on the > SqlRelToRelConverter ? > Also I am thinking about turning off the flatten stage but not sure this is > going to happen (seems like a pandora box kind of flag where you do not > know what to expect) > > On Thu, Oct 24, 2019 at 3:53 AM Igor Guzenko <ihor.huzenko....@gmail.com> > wrote: > > > Hello Naveen, > > > > 1. If I understand correctly, then yes you can extract nested fields from > > struct type. The syntax depends on StructKind value for your data type, > > for example for FULLY_QUALIFIED struct you should first > > make alias for your table and then request nested field like, > > table_alias.struct_column.nested_field. In rel tree such expressions are > > presented as RexCall with SqlItemOperator operator. > > 2. Yes, this ability was implemented in CALCITE-3138 [1]. It builds call to > > ROW type constructor function on top of flattened tree for necessary > > columns. > > 3. Yes, examples of such functions are ROW(...), ANY_VALUE(...) etc. > > > > In current implementation of flattener invocation of ROW constructor > > function is done despite of null handling same issue exists for some > > aggregate function flattening, like COUNT(struct_column). > > Proper null handling is real pain for flattener, original idea was to > > handle special null indicator for each flattened struct, but in practice I > > recognized that it's really hard to deal with flattened fields indices when > > related methods are called from very different points, so for now the > > problem remains unsolved. > > If you can't avoid dealing with null values in your struct columns you > > could try to avoid invocation to SqlToRelConverter.flattenTypes(...) and > > check whether final plan acceptable for you. As far as I know > > there is no reading material for given topic, you can investigate source > > code by debugging RelStructuredTypeFlattener and reading some related plans > > in SqlToRelConverterTest.java and SqlToRelConverterTest.xml. > > > > [1] https://issues.apache.org/jira/browse/CALCITE-3138 > > > > Thanks, > > Igor > > > > On Thu, Oct 24, 2019 at 12:57 PM Naveen Kumar > > <naveenkuma...@flipkart.com.invalid> wrote: > > > > > Hi, > > > > > > I work at Flipkart, we are using Calcite in our streaming platform. In > > most > > > of our use cases, input data is nested. I understand Calcite flattens > > > structs in scan and references fields positionally. > > > > > > I had a few questions on handling nested data - > > > > > > 1. Can RelNode DAG work with nested data (instead of flattened fields) > > > by referencing fields through their nested structure eg, > > > data.order.orderId > > > 2. In the current flattened behavior, can output of a query be a > > struct. > > > Eg if *orderId, orderData.timestamp, orderData.category* are output of > > > select query, can I declaratively organise output to below json > > > structure - > > > 1. > > > > > > > > > > > > > > > > > > *{ "orderId": "order1", "orderData": { "timestamp": 1571904384814, > > > "category": "shoes" } }* > > > 3. Can output of a UDF be struct type > > > > > > Please point me to any reading material or example that would help with > > > these questions. > > > > > > Regards, > > > Naveen > > > > > > -- > > > > > > > > > > > > > > > > > *-----------------------------------------------------------------------------------------* > > > > > > > > > *This email and any files transmitted with it are confidential and > > > intended solely for the use of the individual or entity to whom they are > > > addressed. If you have received this email in error, please notify the > > > system manager. 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