hive querying records for a specific uniontype

Question

I have a sample hive table created as

CREATE TABLE union_test(foo UNIONTYPE<int, double, array<string>, struct<a:int,b:string>>);

The data can be viewed as

SELECT foo FROM union_test;

The output is

{0:1}
{1:2.0}
{2:["three","four"]}
{3:{"a":5,"b":"five"}}
{2:["six","seven"]}
{3:{"a":8,"b":"eight"}}
{0:9}
{1:10.0}

the first field (tag) denotes the type of the union ( 0 for int, 1 for double, 2 for array etc).

My problem is if I found to select only those records where the union type is 2 (array), how should I frame my query?

Answer 1

There is no function in Hive to read data from UnionType. So i wrote 2 UDF´s. One to get Union tag (that you trying to do) and second to get struct from union as an example.

get_union_tag() function:

 package HiveUDF;
 import org.apache.hadoop.hive.ql.exec.Description;
 import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
 import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
 import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
 import org.apache.hadoop.hive.ql.metadata.HiveException;
 import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
 import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
 import org.apache.hadoop.hive.serde2.objectinspector.UnionObjectInspector;
 import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;


 @Description(name = "get_union_tag", value = "_FUNC_(unionObject)"
    + " - Returns union object Tag", extended = "Example:\n" + "  > SELECT _FUNC_(unionObject) FROM src LIMIT 1;\n one")
 public class GetUnionTag extends GenericUDF {  

// Global variables that inspect the input.
// These are set up during the initialize() call, and are then used during the
// calls to evaluate()
private transient UnionObjectInspector uoi;

@Override
// This is what we do in the initialize() method:
// Verify that the input is of the type expected
// Set up the ObjectInspectors for the input in global variables
// Return the ObjectInspector for the output
public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {        

    // Verify the input is of the required type.
    // Set the global variables (the various ObjectInspectors) while we're doing this

    // Exactly one input argument
    if( arguments.length != 1 ){
        throw new UDFArgumentLengthException("_FUNC_(unionObject) accepts exactly one argument.");
    }
    // Is the input an array<>
    if( arguments[0].getCategory() != ObjectInspector.Category.UNION ){
        throw new UDFArgumentTypeException(0,"The single argument to AddExternalIdToPurchaseDetails should be "
                + "Union<>"
                + " but " + arguments[0].getTypeName() + " is found");

    }

    // Store the ObjectInspectors for use later in the evaluate() method
    uoi = ((UnionObjectInspector)arguments[0]);

    // Set up the object inspector for the output, and return it
    return PrimitiveObjectInspectorFactory.javaByteObjectInspector;
}

@Override
public Object evaluate(DeferredObject[] arguments) throws HiveException {

    byte tag =  uoi.getTag(arguments[0].get());
    return tag;
}

@Override
public String getDisplayString(String[] children) {

    StringBuilder sb = new StringBuilder();
    sb.append("get_union_tag(");
    for (int i = 0; i < children.length; i++) {
        if (i > 0) {
            sb.append(',');
        }
        sb.append(children[i]);
    }
    sb.append(')');
    return sb.toString();
}

}

function get_struct_from_union() UDF :

package HiveUDF;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.UnionObjectInspector;

@Description(name = "get_union_struct", value = "_FUNC_(unionObject)"
    + " - Returns struct ", extended = "Example:\n" + "  > _FUNC_(unionObject).value \n 90.0121")
public class GetUnionStruct extends GenericUDF {

// Global variables that inspect the input.
// These are set up during the initialize() call, and are then used during the
// calls to evaluate()
//
// ObjectInspector for the list (input array<>)
// ObjectInspector for the struct<>
// ObjectInspectors for the elements of the struct<>, target, quantity and price
private UnionObjectInspector unionObjectInspector;
private StructObjectInspector structObjectInspector;

@Override
// This is what we do in the initialize() method:
// Verify that the input is of the type expected
// Set up the ObjectInspectors for the input in global variables
// Return the ObjectInspector for the output
public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {        

    // Verify the input is of the required type.
    // Set the global variables (the various ObjectInspectors) while we're doing this

    // Exactly one input argument
    if( arguments.length != 1 ){
        throw new UDFArgumentLengthException("_FUNC_(unionObject) accepts exactly one argument.");
    }
    // Is the input an array<>
    if( arguments[0].getCategory() != ObjectInspector.Category.UNION ){
        throw new UDFArgumentTypeException(0,"The single argument to AddExternalIdToPurchaseDetails should be "
                + "Union<Struct>"
                + " but " + arguments[0].getTypeName() + " is found");

    }        

    // Set up the object inspector for the output, and return it
    return structObjectInspector;
}

@Override
public Object evaluate(DeferredObject[] arguments) throws HiveException {

    return ((UnionObjectInspector) unionObjectInspector).getField(arguments[0].get());
}

@Override
public String getDisplayString(String[] children) {

    StringBuilder sb = new StringBuilder();
    sb.append("get_union_vqtstruct(");
    for (int i = 0; i < children.length; i++) {
        if (i > 0) {
            sb.append(',');
        }
        sb.append(children[i]);
    }
    sb.append(')');
    return sb.toString();
}

}

to use these UDF´s compile and create jar file. Than upload into hive (in my case HDInsight). Than just use

add jar wasb:///hive/HiveGUDF.jar;
CREATE TEMPORARY FUNCTION get_union_struct AS 'HiveUDF.GetUnionStruct';

before u run e.g.

SELECT get_union_tag(exposed) FROM test;