Query A Nested Array in Parquet Records

问题

I am trying different ways to query a record within a array of records and display complete Row as output.

I dont know which nested Object has String "pg". But i want to query on particular object. Whether the object has "pg" or not. If "pg" exist then i want to display that complete row. How to write "spark sql query" on nested objects without specfying the object index.So i dont want to use the index of children.name

My Avro Record:

{
"name": "Parent",
"type":"record",
"fields":[
    {"name": "firstname", "type": "string"},

    {
        "name":"children",
        "type":{
            "type": "array",
            "items":{
                        "name":"child",
                        "type":"record",
                        "fields":[
                            {"name":"name", "type":"string"}
                        ]
                    }
            }
    }
]
}

I am using Spark SQL context to query dataframe which is read. So if input is

Row no   Firstname Children.name
    1    John       Max
                    Pg
    2    Bru        huna
                    aman

Output should return poq 1 since it has row where one object of children.name is pg.

val results = sqlc.sql("SELECT firstname, children.name FROM nestedread where children.name = 'pg'")
results.foreach(x=> println(x(0), x(1).toString))

The above query doesn't work. but it works when i query children[1].name.

I ALSO want to know that if i can filter a set of records and then explode. Instead of first explode and create large number of rows and then filter.

回答1:

It seems that you can use

org.apache.spark.sql.functions.explode(e: Column): Column

for example in my project(in java), i have nested json like this:

{
    "error": [],
    "trajet": [
        {
            "something": "value"
        }
    ],
    "infos": [
        {
            "something": "value"
        }
    ],
    "timeseries": [
        {
            "something_0": "value_0",
            "something_1": "value_1",
            ...
            "something_n": "value_n"
        }
    ]
}

and i wanted to analyse datas in "timeseries", so i did:

DataFrame ts = jsonDF.select(org.apache.spark.sql.functions.explode(jsonDF.col("timeseries")).as("t"))
                     .select("t.something_0",
                             "t.something_1",
                             ...
                             "t.something_n");

I'm new to spark too. Hope this could give you a hint.

回答2:

The problem was solved by

I found a way through Explode.

val results = sqlc.sql("SELECT firstname, child.name, FROM parent LATERAL VIEW explode(children) childTable AS child

来源：https://stackoverflow.com/questions/37270703/query-a-nested-array-in-parquet-records

标签

apache-spark

apache-spark-sql

hiveql

spark-dataframe

parquet