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How to use lateral view explode in Hive for XML data format?

由 ╄→гoц情女王★ 提交于 2019-12-25 03:29:39

问题


I am trying to load sales data which is in XML format to the Hive table. Below is a small sample of the data.

I am aware that I can load the data below to Hive if I separate it to several tables and then join them as required. But just wanted to know if I can load them in a single table and the expected output should look like the screenshot attached.

Please help me with the table structure I should use and how can I use the lateral view explode option effectively to achieve this.

Sample data:

  <Store>
    <Version>1.1</Version>
    <StoreId>16695</StoreId>    
    <Bskt>
      <TillNo>4</TillNo>
      <BsktNo>1753</BsktNo>
      <DateTime>2017-10-31T11:19:34.000+11:00</DateTime>
      <OpID>50056</OpID>
      <Itm>
        <ItmSeq>1</ItmSeq>
        <GTIN>29559</GTIN>
        <ItmDsc>CHOCALATE</ItmDsc>
      <ItmProm>
          <PromCD>CM</PromCD>
        </ItmProm>
      </Itm>
      <Itm>
        <ItmSeq>2</ItmSeq>
        <GTIN>59653</GTIN>
        <ItmDsc>CORN FLAKES</ItmDsc>
      </Itm>
        <Itm>
        <ItmSeq>3</ItmSeq>
        <GTIN>42260</GTIN>
        <ItmDsc> MILK CHOCOLATE 162GM</ItmDsc>
        <ItmProm>
          <PromCD>MTSRO</PromCD>
          <OfferID>11766</OfferID>
        </ItmProm>
      </Itm>
    </Bskt>
    <Bskt>
      <TillNo>5</TillNo>
      <BsktNo>1947</BsktNo>
      <DateTime>2017-10-31T16:24:59.000+11:00</DateTime>
      <OpID>50063</OpID>
      <Itm>
        <ItmSeq>1</ItmSeq>
        <GTIN>24064</GTIN>
        <ItmDsc>TOMATOES 2KG</ItmDsc>
        <ItmProm>
          <PromCD>INSTORE</PromCD>
        </ItmProm>
      </Itm>
      <Itm>
        <ItmSeq>2</ItmSeq>
        <GTIN>81287</GTIN>
        <ItmDsc>ROTHMANS BLUE</ItmDsc>
        <ItmProm>
          <PromCD>TF</PromCD>
        </ItmProm>
      </Itm>
    </Bskt>
  </Store>

Desired Output

enter image description here

Table structure:

CREATE EXTERNAL TABLE IF NOT EXISTS POC_BASKET_ITEM_PROMO (
`Version` string,
`StoreId` string,
`DateTime` array<string>,
`BsktNo` array<double>,
`TillNo` array<int>,
`Item_Seq_num` array<int>,
`GTIN` array<string>,
`ItmDsc` array<string>,
`Promo_CD` array<string>,
`Offer_ID` array<int>
)

ROW FORMAT SERDE 'com.ibm.spss.hive.serde2.xml.XmlSerDe'
WITH SERDEPROPERTIES (

"column.xpath.Version"="/Store/Version/text()",
"column.xpath.StoreId"="/Store/StoreId/text()",
"column.xpath.DateTime"="/Store/Bskt/DateTime/text()",
"column.xpath.BsktNo"="/Store/Bskt/BsktNo/text()",
"column.xpath.TillNo"="/Store/Bskt/TillNo/text()",
"column.xpath.Item_Seq_num"="/Store/Bskt/Itm/ItmSeq/text()",
"column.xpath.GTIN"="/Store/Bskt/Itm/GTIN/text()",
"column.xpath.ItmDsc"="/Store/Bskt/Itm/ItmDsc/text()",
"column.xpath.Promo_CD"="/Store/Bskt/Itm/ItmProm/PromCD/text()",
"column.xpath.Offer_ID"="/Store/Bskt/Itm/ItmProm/OfferID/text()"
)

STORED AS INPUTFORMAT 'com.ibm.spss.hive.serde2.xml.XmlInputFormat'
    OUTPUTFORMAT 
'org.apache.hadoop.hive.ql.io.parquet.MapredParquetOutputFormat' 
    LOCATION 'hdfs://namenode:8020/DEV/TEST/nanda_test'
    TBLPROPERTIES (
    "xmlinput.start"="<Store","xmlinput.end"="</Store>"
);

Output: enter image description here

Tried below query to read the data, It is not showing the results in the way i want.

select Version,StoreId,basket_dtm,basket_number,till_number from POC_BASKET_ITEM_PROMO
    LATERAL VIEW explode(DateTime) table1 as basket_dtm 
    LATERAL VIEW explode(BsktNo) table2 as basket_number
    LATERAL VIEW explode(TillNo) table3 as till_number;

Results:

enter image description here


回答1:


Explode for array object works like cross join. So if you have 3 columns with each containing array with 2 elements, applying explode on all the columns will give you 8 rows.

You can't map one object from array to another.

Actually you can by using posexplode which gives you index for each element. which you can use to join based on condition. However, that' tricky when you have multiple columns and the array size is different for each column.

Solution

  • Use posexplode if you have less column to explode and array size is same. for your case this is not going to work. So
  • Store XML as Complex Data Type : Store your whole XML as a complex data type (not just array), I am talking about creating a struct based on your xml. If you don't have much complex xml, you can achieve this. However xmlSerde is not as good as JSONserde when it comes to converting file to complex data type.

So in your case best solution would be.

  • Convert your XML to JSON. You can use NiFi or some other technology for that.
  • Create Hive table using JSONserde and load this file.
  • Create a view as per your requirement.

JSON for Your XML

{"Version":"1.1","StoreId":"16695","Bskt":[{"TillNo":"4","BsktNo":"1753","DateTime":"2017-10-31T11:19:34.000+11:00","OpID":"50056","Itm":[{"ItmSeq":"1","GTIN":"29559","ItmDsc":"CHOCALATE","ItmProm":{"PromCD":"CM"}},{"ItmSeq":"2","GTIN":"59653","ItmDsc":"CORNFLAKES"},{"ItmSeq":"3","GTIN":"42260","ItmDsc":"MILKCHOCOLATE162GM","ItmProm":{"PromCD":"MTSRO","OfferID":"11766"}}]},{"TillNo":"5","BsktNo":"1947","DateTime":"2017-10-31T16:24:59.000+11:00","OpID":"50063","Itm":[{"ItmSeq":"1","GTIN":"24064","ItmDsc":"TOMATOES2KG","ItmProm":{"PromCD":"INSTORE"}},{"ItmSeq":"2","GTIN":"81287","ItmDsc":"ROTHMANSBLUE","ItmProm":{"PromCD":"TF"}}]}]}

JsonSerde might give your error if you have tabs or other white spaces in your file. So it's always best to remove them.

Hive Table

create external table temp.test_json
(
Version string,
StoreId string,
Bskt array<struct<
                    BsktNo:string,
                    DateTime:string,
                    OpID:string,
                    TillNo:string,
                    Itm:array<struct<
                                        GTIN:string,
                                        ItmDsc:string,
                                        ItmSeq:string,
                                        ItmProm:struct<
                                                        OfferID:string,
                                                        PromCD:string
                                                        >

                                    >
                            >
                >
            >
)
row format serde 'org.openx.data.jsonserde.JsonSerDe'
location '/tmp/test_json/table/';

Create View

SELECT Version,
         StoreId,
         basket.bsktno,
         basket.tillno,
         basket.`datetime`,
         item.itmseq,
         item.itmdsc,
         item.gtin,
         item.itmprom.offerid,
         item.itmprom.promcd
FROM temp.test_json 
lateral view explode(bskt) b AS basket 
lateral view explode(basket.itm) i AS item




回答2:


Thanks for detailed solution. I tested it and it worked perfectly fine. I tried a similar approach to read the data from the XML directly with XML serde.

My challenges:

1)XML to JSON conversion takes additional development efforts and we don't have Apache Nifi installation parcels in Cloudera by default, we need to install it with custom parcels.
2) My data will definitely have spaces/tab spaces in it, especially in 'Item description' field.We need to load the data with the same names as we receive. So converting to JSON and use the 'org.openx.data.jsonserde.JsonSerDe' didn't help. Queries failed with errors as suggested by you.

Below is the Hive table structure and the query I am using to read the data. I am able to explode the first level array (Bskt) successfully without any issues.

But when i try to explode the second level array (Itm) it returns NULL results for all the fields in 'Itm'.

Is there any issue with my query or the table structure itself?

create external table nanda_scan_xml  (
  Version string,
  StoreId string,
  Bskt array<struct<
                    Bskt:struct<
                                DateTime:string,
                                TillNo:string,
                                BsktNo:string,
                                Itm:array<struct<
                                                Itm:struct<
                                                    ItmSeq:string,      
                                                    GTIN:string,        
                                                    ItmDsc:string,      
                                                    DeptCD:string,      
                                                    ItmCD:string,       
                                                    SalesQTY:string,        
                                                    SalesExGST:string,      
                                                    Points:string,      
                                                    CostExGST:string,       
                                                    GSTRate:string,     
                                                    DiscAmtExGST:string,        
                                                    ItmProm:struct<     
                                                                    PromCD:string,      
                                                                    OfferID:string      
                                                                  >
                                                              >
                                                     >
                                            >
                                >
                    >
            >
)
row format serde 'com.ibm.spss.hive.serde2.xml.XmlSerDe'
with serdeproperties 
(
    "column.xpath.Version"       = "/Store/Version/text()",
    "column.xpath.StoreId"       = "/Store/StoreId/text()",
    "column.xpath.Bskt"  = "/Store/Bskt"

)
stored as 
inputformat     'com.ibm.spss.hive.serde2.xml.XmlInputFormat'
outputformat    'org.apache.hadoop.hive.ql.io.parquet.MapredParquetOutputFormat' 
LOCATION 'hdfs://namenode/LandingArea/Sources/SCANP/IGA_SCAN/STAGING/'
tblproperties 
(
    "xmlinput.start"    = "<Store>",
    "xmlinput.end"      = "</Store>"
);

Query:

1)For Bskt which works fine:

SELECT  Version,
        StoreId,
        basket.Bskt.DateTime,
        basket.Bskt.bsktno,
        basket.Bskt.tillno
FROM eim_stg.nanda_scan_xml
LATERAL VIEW EXPLODE(Bskt) b AS basket;

Results:

enter image description here 2) When trying two lateral view explode in a single query:

SELECT  Version,
        StoreId,
        basket.Bskt.DateTime,
        basket.Bskt.bsktno,
        basket.Bskt.tillno,
        item.Itm.ItmSeq,
        item.Itm.ItmDsc,
        item.Itm.GTIN,
        item.Itm.itmprom.OfferID,
        item.Itm.itmprom.PromCD 
FROM eim_stg.nanda_scan_xml
LATERAL VIEW EXPLODE(Bskt) b AS basket
LATERAL VIEW EXPLODE(basket.Bskt.Itm) i AS item limit 100;

Results:

enter image description here

3) Query:

SELECT  Version,
        StoreId,
        basket.Bskt.DateTime,
        basket.Bskt.bsktno,
        basket.Bskt.tillno,
        item.Itm.ItmSeq,
        item.Itm.ItmDsc,
        item.Itm.GTIN,
        item.Itm.itmprom.OfferID,
        item.Itm.itmprom.PromCD 
FROM eim_stg.nanda_scan_xml
LATERAL VIEW EXPLODE(Bskt) b AS basket
LATERAL VIEW EXPLODE(basket.Itm) i AS item limit 100;

Error:

enter image description here



来源：https://stackoverflow.com/questions/53384728/how-to-use-lateral-view-explode-in-hive-for-xml-data-format

标签
xml
parsing
Hadoop
Hive
explode
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